The good news is even if you started an amendment, nothing will be affected permanently because you have to print and mail to file an amendment, you cannot e-file. Your original return is still the last one on file.
The following TurboTax FAQ helps outline how to cancel an amended return using TurboTax Online:
https://ttlc.intuit.com/replies/4170678
Please refer to this TurboTax FAQ if you are needing to cancel an amended return using TurboTax CD/Download Software:
https://ttlc.intuit.com/replies/4170766
