My underpayment penalty went from under $200 to over $2,000 while I was trying out the options. How can I return to the original penalty?

The best thing to do at this point is go to delete a form and delete the 2210.  You may have to look for Worksheets with Estimated Tax as well.

Windows instructions

1. Open or continue your return.
2. Switch to Forms Mode by selecting the Forms icon.
3. From the menu, select the form you want to remove.
4. After the form is generated in the right pane, select the Delete Form button.
5. Follow any onscreen instructions to remove the form or forms.

Mac instructions

1. Open or continue your return.
2. Switch to Forms Mode by selecting the Forms icon.
3. From the menu, select the form you want to remove (if you don't see it, select Open Form at the top).
4. From the Forms menu, select Remove [form name].
5. Follow any onscreen instructions to remove the form or forms.

For those using TT Online: Go to Tax Tools > Tools to find the Delete Form option.