it really depends
ftba is based on both of you - if your combined total is less than estimated, no overpayment will occur there
ftbb is based on lower income earner. i am assuming that is you
(not sure with the way you've worded if your income was significantly more or less than estimated so i'll do both scenrios

if you earned more than estimated (est at 10k, actual at 20k) you will have an overpayment
if you earned less than estimated (est at 20k, actual at 10k) you will get a top up

if you come under scenario 1, your overpayment will come out of supplements first, so you may not have an actual debt, just less of a top up