Since the difference is exactly double then you must look at the 1040X to see if you did it correctly ... did you change the line 18 amount to zero ? If so that is the error.
Look at the form 1040X …
Column A should have the figures from the original return, Column C the corrected figures and Column B the differences between the other 2 which needs an explanation on page 2 of the form 1040X.
If you completed it correctly you will see an entry on either line 16 OR 18:
On line 16 should be the amount you paid with your original return.
On line 18 should be the amount of your original refund you received.
Then you will see your extra refund on line 22 OR the new balance due you need to pay on line 20.
