You can probably get away with it if you added it now.
If it were me, I'd quickly boil a gallon, cool it quick in the sink, and add it in an hour or so.
If you add straight water now, you will worry if you screwed it up. It will probably be OK, but might not be.
Oxidizing beer results in poor storage life, and the beer going stale quickly. Might taste great fresh, but after a few weeks/months may start to taste stale.