You actually have a filing requirement if any of the first time homebuyer credit is subject to recapture (i.e. repayment). Besides the gross income rules, there are several other things which may require a filing of a return. See the link below for IRS Form 1040 Instructions (page 10, Chart C - Other Situations when you must file.) You will prepare your return and the pay the recapture amount with your return.
IRS Form 1040 instructions
https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
