I transposed a number in box 2 (not in my favor), it won't let me correct it at this stage. how do I correct it?

You will have to delete the form (Form W-2?) using the "Delete a Form" tool, and re-enter it in the appropriate (W-2?) interview.

See: How do I delete forms in TurboTax Online?

After deleting this form, log out of the program. When you log back in, you use the Delete a Form tool to see if it has been removed from the list of forms in your return. If it has, you should be able to re-enter it correctly and complete your return.

If the delete and re-enter process does not allow you to correct the problem, you may have to try Using Clear & Start Over in TurboTax Online

Why does this happen? Once you enter (or import or transfer) certain information, the program creates or updates forms and worksheets that use that information. In many cases, you cannot "change" that information in the interview process - in a manner of speaking, it has been "written in ink" on the forms. You have to delete the form and any associated worksheets in order to correct.