I think you can just start. They've already been online I believe, and with just 3 you can keep them in mind if they don't post in 1-2 days
You never stated it was obligatory to confirm, I think they don't expect it's necessary
Thank you for reacting so kindly. It was really so hard not to tell anyone about it for all this ti-- wait what? Oh, haha you mean the sign ups...
Awkward..