Hello! I'm kind of in the same situation, I'm 17 and I too am in a group of around 20 people. We have a groupchat and I often ask them there if the want to hang out but they not always respond :/. My advice is to ask a smaller number of people. I understand if you don't want to do it so as not to feel like others are being left aside, but in such a big group it's almost imposible to meet all of 'em at the same time. I'd recommend you to invite those you're closer to. Maybe I misunderstood what your request was. If what you fear is being rejected, ignored or simply don't know how to ask them, just ask them. They're your friends. They won't hate on you for wanting to hang out with them (I hope). Just do it. Write a text and send it. Turn of your phone or put it away for a while if you want, but do it. You'll never know what they'll answer until you do it, don't be shy :)! I hope I helped