Get your taxes done using TurboTax

The program will not stop you from trying to file 2 1040 returns but the IRS will ... so did you file one 1040 and one amended 1040X return ?    Were they both accepted for processing by the IRS ?   If so you cannot stop either return.   If you need to make changes then you must wait for the original return AND the amended return to be fully processed before you can file yet  another amended return.