SQL Developer script output truncates sys_refcursor width

Not directly answering the question - I don't know why the behaviour is different or how to change it when calling the function from a query, other than with a column command to set the width, using an alias here to simplify things slightly:

set lines 250
column rc format a250
select my_function(input1,input2,input3) as rc from dual;

But you can also get the output you want by calling the function differently; with a variable and an anonymous block (or execute as shorthand):

variable rc refcursor;
exec :rc := MY_FUNCTION(input1,input2,input3);
print rc

Well, almost as you want it; the first line of the output is the variable name rather than the function/parameter list; but the cursor columns are not wrapped:

anonymous block completed
RC
---------------------------------------------------------------------------
COLUMN1                   COLUMN2 COLUMN3    COLUMN4    COLUMN5    
------------------------- ------- ---------- ---------- ---------- 
18-NOV-14                 text    some_data1 some_data2 some_data3 

You can also run your function from the code editor (rather than the worksheet), which generates an anonymous block for you; when you click the run arrow (or hit control-F10) you get a dialog like this:

And after running it you get an 'output variables' tab at the bottom of the main window which shows the cursor output in a grid.

You can also see the grid view when you run select my_function(...) from dual. The cursor goes into the normal 'query result' window but not in a very friendly form, appearing as something like:

{<COLUMN1=19-NOV-14,COLUMN2=text,COLUMN3=some_data1,COLUMN4=some_data2,COLUMN5=some_data3>,}

But if you double-click a value then you see a yellow pencil symbol at the far right of the column, and clicking that shows that cursor in its own grid.

Personally I prefer the print option in the script output but I rarely use the gird displays anyway.