Probably fine to just leave it. But what style beer is it? Your bitterness might be a bit higher than planned, so if it is lightly bittered you might want to dilute it to get the right balance. If it's something like a big IPA or APA, don't mess with it. The extra bitterness (which is probably minimal to begin with) will probably not be noticed and the extra ABV will onyl help!
I had efficiency problems on an English pale and had to boil off a bunch to get the same OG, around 3.75 gallons instead of 5. I didn't think to adjust the hops and it is certainly more bitter than it was supposed to be. But it's a good thing I like hops, the beer is still very good.
EDIT: Probably best to wait until fermentation is fully done to think about dilution. If you still get close to the recipe's FG, best to leave as is.