First 7 is all you need for the credits ... so nothing would change if correct that number.
Next as to how it happened ... most likely when you were reviewing in the interview mode ... when you were on that screen you probably went to scroll down to click on the continue button but the cursor was on that entry box thus you accidentally changed the number of months ( too common a mistake I make a lot).
Before you file always save a PDF and review the forms that way, do not use the interview process.
