Everything can be cleared by deleting the IRA Contributions Worksheet: Click My Account -> Tools -> Delete a form, then click the Delete link next to IRA Contrib Wks.
First, though, it would be informative to find out where things went wrong. You might find that you also entered a $1,020 return of contribution prior to deciding to recharacterize to a traditional IRA instead. In fact, I'll bet that that is what happened since I can reproduce your result this way. That would appear as $1,020 on line 26 of the IRA Contrib Wks. Unfortunately, with no excess contribution remaining, TurboTax will not present the step-by-step page that would allow you to delete the indication that you will have $1,020 of the contribution returned.
Before the deleting the IRA Contrib Wks, try this to force TurboTax to display the potentially offending entry: Change your Roth IRA contribution entry from $4,000 to $10,000 to ensure that TurboTax detects an excess contribution. Proceed to the You Currently Have a Penalty page where I bet you'll see $1,020 that you need to delete. After deleting the $1,020 entry here, go back though and change the $10,000 back to the correct amount of $4,000.
