Firstly, welcome to the forums!
I went to a Catholic school too but thankfully different points of view were completely tolerated. I never had any problems with my choice to not receive communion and so it's really unfortunate that you're facing such intolerance towards your views. Personally, I believe that you should stand up for free speech and for your right to be an atheist. You shouldn't let yourself be told what you have to believe in nor should you feel that you are unable to voice your preferences when it comes to receiving communion.
I wish you all the best and feel free to join in the discussion here with other atheists if it helps you to be more confident in your views

I went to a Catholic school too but thankfully different points of view were completely tolerated. I never had any problems with my choice to not receive communion and so it's really unfortunate that you're facing such intolerance towards your views. Personally, I believe that you should stand up for free speech and for your right to be an atheist. You shouldn't let yourself be told what you have to believe in nor should you feel that you are unable to voice your preferences when it comes to receiving communion.
I wish you all the best and feel free to join in the discussion here with other atheists if it helps you to be more confident in your views

"The chances of each of us coming into existence are infinitesimally small, and even though we shall all die some day, we should count ourselves fantastically lucky to get our decades in the sun." - Richard Dawkins