am i wrong for not wanting to be a third wheel?

ok so i have these 2 friends that are dating right? and because on of their parents is really homophobic and not supportive of the relationship, they can't go out in public together without another friend or "chaperone" because their parents think that they're gonna do the nasty. so when they asked if i would come with them on their pool date, i said yes, because they're both my friends and i want them to be able to go out together. so since i figured that they would probably not want to hang out with the third wheel, "chaperone friend" if you might, i asked my best friend if she would come along, because it is just to the YMCA pool. i know normally i would obviously ask the friends that asked me before i invited my other friend, but since i'm just the excuse they have to go out together i figured it wouldn't be a big deal anyway. but now one of my friends that originally asked me to go with them seems mad at me. they said it's fine and their girlfriend doesn't have an issue with it, but i still don't know?