Why is RSA encryption in Java producing different length ciphertext than C#

I am AES encrypting some text using a randomly generated key and then RSA encrypting that key with a private key so that I can upload it to a database.

The RSA keys are generated using KeyPairGenerator in Java and saved as a file. Keys are read in using File.ReadAllBytes().

When I do this in Java everything works perfectly and the encrypted key is always 172 bytes, but when I do it in C# the encrypted key is always 844 bytes. I'm pretty sure the text is being encrypted properly using AES, but something is going wrong with the RSA encryption.

I have checked the key sizes in Java and C# and they always match. Literally, the only difference I can see is the RSA encrypted ciphertext length, which makes the data unusable. I believe it has something to do with padding, but I don't know how to fix it.

Java

public String encryptText(String msg, PrivateKey key) 
            throws NoSuchAlgorithmException, NoSuchPaddingException,
            UnsupportedEncodingException, IllegalBlockSizeException, 
            BadPaddingException, InvalidKeyException {

        KeyGenerator generator;   
        this.cipher.init(Cipher.ENCRYPT_MODE, key); //cipher is initialized earlier with this.cipher = Cipher.getInstance("RSA");

            try {
                generator = KeyGenerator.getInstance(AES);
                generator.init(128); // The AES key size in number of bits
                SecretKey secKey = generator.generateKey();

                Cipher aesCipher = Cipher.getInstance(AES);
                aesCipher.init(Cipher.ENCRYPT_MODE, secKey);

                String encText = Base64.getEncoder().encodeToString(aesCipher.doFinal(msg.getBytes("UTF-8")));
                String encKey = Base64.getEncoder().encodeToString(cipher.doFinal(secKey.getEncoded()));

                return "(" + encText + ")" + encKey;                
            } catch (NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException | IllegalBlockSizeException | BadPaddingException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        return null;
    }

C#

public String EncryptText(byte[] privateKeyBytes, string msg)
        {
            try
            {
                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
                RSAParameters RSAKeyInfo = RSA.ExportParameters(false);

                RSAKeyInfo.Modulus = privateKeyBytes;
                RSA.ImportParameters(RSAKeyInfo);

                RijndaelManaged aes = new RijndaelManaged();
                aes.BlockSize = 128;
                aes.KeySize = 128;
                aes.Mode = CipherMode.ECB;
                byte[] keyGenerated = aes.Key;

                string keyStr = Convert.ToBase64String(keyGenerated);
                byte[] keyArr = Convert.FromBase64String(keyStr);
                byte[] KeyArrBytes16Value = new byte[16];
                Array.Copy(keyArr, KeyArrBytes16Value, 16);

                aes.Key = KeyArrBytes16Value;

                ICryptoTransform encrypto = aes.CreateEncryptor();

                byte[] plainTextByte = ASCIIEncoding.UTF8.GetBytes(msg);
                byte[] CipherText = encrypto.TransformFinalBlock(plainTextByte, 0, plainTextByte.Length);

                string encText = Convert.ToBase64String(CipherText);
                string encKey = Convert.ToBase64String(RSA.Encrypt(aes.Key, true));

                return "(" + encText + ")" + encKey;

            }
            catch (CryptographicException e)
            {
                Console.WriteLine("FAILED: " + e.Message);
            }

            return null;
        }

UPDATE
Thanks to Henno for pointing out that the problem was in how I was reading the key. I ended up using Bouncy Castle to handle the RSA encryption in C#. I also changed my java code to encrypt with the public key instead of the private key.

New C#

public String EncryptText(byte[] keyBytes, string msg)
        {
            try
            {
                AsymmetricKeyParameter asymmetricKeyParameter = PublicKeyFactory.CreateKey(keyBytes);
                RsaKeyParameters rsaKeyParameters = (RsaKeyParameters)asymmetricKeyParameter;
                RSAParameters rsaParameters = new RSAParameters();
                rsaParameters.Modulus = rsaKeyParameters.Modulus.ToByteArrayUnsigned();
                rsaParameters.Exponent = rsaKeyParameters.Exponent.ToByteArrayUnsigned();
                RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
                rsa.ImportParameters(rsaParameters);

                RijndaelManaged aes = new RijndaelManaged();
                aes.BlockSize = 128;
                aes.KeySize = 128;
                aes.Mode = CipherMode.ECB;
                byte[] keyGenerated = aes.Key;

                string keyStr = Convert.ToBase64String(keyGenerated);
                byte[] keyArr = Convert.FromBase64String(keyStr);
                byte[] KeyArrBytes16Value = new byte[16];
                Array.Copy(keyArr, KeyArrBytes16Value, 16);

                aes.Key = KeyArrBytes16Value;

                ICryptoTransform encrypto = aes.CreateEncryptor();

                byte[] plainTextByte = ASCIIEncoding.UTF8.GetBytes(msg);
                byte[] CipherText = encrypto.TransformFinalBlock(plainTextByte, 0, plainTextByte.Length);

                string encText = Convert.ToBase64String(CipherText);
                string encKey = Convert.ToBase64String(rsa.Encrypt(aes.Key, false));

                return "(" + encText + ")" + encKey;

            }
            catch (CryptographicException e)
            {
                Console.WriteLine("FAILED: " + e.Message);
            }

            return null;
        }