First BIAB gravity question

First biab. My volume calculator must be screwed up! Anyway, i boiled longer to get down to what I thought was 5 gallons. (15 gal pot). Ended up being just 4 gallons. But, at that point, my OG was spot on. But, I elected to top it off in the fermentor to 5 gallons before pitching. Which obviously messed up my OG. Should I have left it at 4 gallons at the right OG? Or ok to top off? Its a belgian wit. Thx for help.

I would say to have left it at the 4 gallons if it was at the correct OG.

Crap, thats what I was afraid of.

Relax. You still made beer....just beer that is a bit watered down