Like most have said, I wouldn't take them with your mom or at a concert, but given the fact that you seem like you are going to anyways...
Well, different people react different to shrooms and also, some shrooms are much stronger than others.
Me personally, I've done shrooms 10 times and I only got LOTS of visuals the first time, and a few the second.
The other 8 times I've gotten no visuals off even an 8th, which I didn't like...but personally for me, I find shrooms to be very relaxing and not at all like LSD.
I can take shrooms by myself and for me I feel less anxiety and actually in a way, less fucked up (well unless I get visuals like the first time) than I do even when high on weed.
For me it's like I get totally clear headed and feel like everything is perfect in the world and I could probably be normal around others if not for my dilated pupils.
But you can't be sure you'll react that way, and many people don't, and I don't even think I would on a stronger batch of shrooms like my first time, or if I took more.
So...my answer would be, if you absolutely HAVE to take shrooms with your mom....take 1 gram...maybe 1.5.
Even if they are very strong shrooms I don't think 1-1.5 grams should be anything overwhelming or make you feel SO much more fucked up than if you smoked a lot of weed...just a different high.
Personally, if you are comfortable carrying them around on you while at the concert which I WOULD NOT AT ALL RECOMMEND BECAUSE I DON'T WANT YOU GETTING ARRESTED....
But if you ARE....the best possible option is probably to dose very low....just take 1 gram...and wait a little more than an hour to see how you feel since they take about 45 mins to kick in.
If after about 1 hour and 15--90mins you feel relaxed and good, take another gram or another half a gram, but I wouldn't suggest the whole 8th.
If you are leaving the shrooms at home, which I recommend, then take less than 2 grams, and I'd guess if you have experience on acid it won't be anything you can't handle, but be prepared that your mom might figure it out, and if she does...well, that's on you to decide how to deal with it..........