You should be good though alcohol will be 0.5% or so lower but should still be good. There are pluses to topping off (less chance of oxidation). But just make your pre-boil a bit bigger next time. My first batch was 5.5 gal. My second was 4.6 gal. I didn't top off but left it ride. 4 beers in volume didn't matter as much to me as hitting my numbers.
Let me know how it turns out. Are you whole leaf hopping or using pellets? I don't know if I can find whole hops here in MS. Planning on visiting the lhbs for the first time in a few weeks.
