Ipad is not accepting my icloud, despite the fact that is the icloud it needs

Hello. My name is Henry Chmielefski. Not too long ago, I received an ipad from a charity known as Lisa's Army. Among other things, they gifted me an ipad. I have used it for a bit now, and I have enjoyed it. Recently, my ipad has gone into a mode called activation lock. It says to use my iclound account, which I do, and it says it's not the right account, despite the fact that this is the account it needs. What do I do?