Also a chronic weed user (45m)… brother, weed will fuck you up at a young age. Massively!  When I use weed occasionally then yes it chills me out. When I smoke all day every day (most of the time) it actually gives me chronic anxiety. I had the same issues in uni with public speaking and my way of dealing with it was to do the absolute bare minimum required and take the shitty grade (try to make up for it with the other work)  What I wish I had done is speak to the professors and/or councillors, tell them my problems and ask for concessions. I would strongly advise to go down this route, and see what they say. You have nothing to lose and everything to gain. Good luck!