If you're uncomfortable, I wouldn't call them. I'd maybe go to a few more meetings, get to know them in person better first. I'm not good with phones and calling people. I don't think they'll ask you why you didn't call but if they do, just explain vaguely that you were busy this week or say you "thought about it" but when you looked at the clock it was too late, some vaguely friendly, polite reply :-)