No you can't. Don't be scared.
It's not uncommon to feel like you're dying as the world dissolves away. You can lose all sense of self etc. at high doses and if you can learn to relax and let go, even though it seems like you 'shouldn't', it can be even more wonderful. I have cried many times after smoking DMT. Once I thought I had actually died and I was so relieved to be back. But it shows you what you have all around you, right? Love
Have fun at your graduation!!!
You should do it sitting down or lying down. Don't get up. Just remember that nothing can go wrong, no one has ever died from smoking DMT. Your 20 smokes were just a warm-up! Embrace infinity! And then come back! Then embrace infinity etc. Don't hold on to thoughts, let them flow, come-and-go, you'll have no worries and you can slide in and out effortlessly. Thinking and DMT smoking don't mix too well; nor does running around really! Hope you're well now, though.

It goes from your system in no time, so you'll be fine.
May not be appropriate
right now for OP, but maybe later:
If you want to go further, clear your mind of thoughts as much as possible, smoke a little bit to get 'the feel' for it - which will relax you as well - and then keep puffin' 'till you're fully dissolved.
I always eyeball it. There's no point not having enough fuel in the rocket! All aboard the Dreamland Choo-Choo!!! I've smoked stupid amounts and I've honestly never died once. Or if I did I came back - so same difference really!

Jump in; no fear! (Maybe not
right now. But next time!)