please help! bottle confusion!

My baby is 9 months! Him and his cousin have the same bottle, although his cousin is 2 and drinks regular cow milk, my son drinks powdered similac!  Bottle confusion happened and I accidentally gave my son his cousins bottle! ☹️☹️😫 what's the worst that can happen to my son?! I know at age 1 he can start drinking real milk! Scared! Has this happened to anyone?!! He's feeling okay! Hasn't gotten diarrhea?! What's the worst that can happen!? It was a 8fl oz bottle!