I need help for my future university life!!!!!!! 2 important questions?

Im in grade 12 and have applied to university for mathematical stuff and right now i want to be an actuary. But I am sort of doubting myself because I want to have a job that helps the world out. I want a job that can help people out and make the world somewhat a better place. So i just wanted to know the impact that actuaries have on the world. I dont want to enter a field that is all about the money, even though actuaries work with insurance. I was thinking of becoming an engineer for a while however right now i am taking physics which is brutally killing me. I mean im ping but im not understanding as much as i would like. It is weird because I am doing well in my Calculus, right now i have an 81 avg and my last test I got an 88. And in my adv. functions Im doing great as well, but physics is just hurting me. Which is why I am doubtful about entering engineering. This leads me to my other question which is whether universities take into consideration that physics is hard or not when deciding to accept you or not. Like i know that this will drop my average and am a little scared because i hope to go to a university which has an admission avg. of low 80s (University of Waterloo) for actuarial science. So these are my two questions. Ill be grateful if anyone can answer one of them or both. Thank you!!