You can't cancel once you transmit**.
Your returns won't be different unless you made an error on one or the other. Since you have already filed, you can print a copy of your tax form from Turbotax. If you can also print your form from the other service, compare them side by side to see what the differences are. If you find you did make an error on your Turbotax return, you can amend the return to correct the error and claim any additional refund, but amended returns won't be fileable until March.
(**If the IRS rejects your return, such as for a social security or birthdate mismatch, it will be returned to you unfiled, and you can make any changes you like before transmitting it again. But you can't cancel a transmitted return yourself.)
