Can I cancel my e filed but not accepted return

[VolvoGirl]

No.  Only if the IRS rejects it when they open on Jan 26 (unless they take some returns earlier to test).   If they accept it then you need to wait for them to fully process it and send the refund or you pay the tax due.   Then you can Amend to change it.   

[mesquitebean]

Did you actually go all the way to the end and click on the "Transmit returns now" button?   If you actually transmitted the return, and it has a status of "pending," there's nothing you can do but wait to see if it is accepted or rejected by the IRS for processing.  If rejected, then you can either fix it, start over, or abandon it and file it elsewhere, etc.   If accepted by the IRS, however, then the only way to correct anything is to file an amended return.   So if you didn't want to efile it, then you can hope it is ultimately rejected, then you can do what you want.  If accepted, then you can amend it.

The IRS opens up and starts accepting/rejecting returns on January 26, except for a few returns they may pull early.  The majority of early-filed returns will sit on TurboTax servers until pulled by the IRS on/after January 26.