I'm glakit

Ok, I’ve been brewing for a while, extract kits by myself and all grain with a buddy. Finally upgraded and brewed all grain last night by myself. Everything went perfect, sanitization excellent, I hit all my temps etc. When I went to bed last night I was feeling pretty good about myself.

I checked my primary this morning and discovered that I forgot to put the top dome cap on my air lock. I sanitized one as soon as I noticed and put it on but this means my wort was exposed to air through the small hole in the airlock for about 12 hours.

The airlock is bubbling now but have I ruined the batch?

No, the yeast will use whatever O2 they need and the rest will be pushed out of the fermenter by the CO2 from fermentation.

You’ll be fine.