Magu if you want a strong self working effect, try "Out Of This World" by Paul Curry,it is an easy but strong effect to perform. Lots of room for presentation.
To find out if your effect is original try researching it on the web. Or show the effect to known magician or magic shop that might have an idea if it's original.
I'm pretty certain you can do other tricks if you still have the gimmick in the deck. You can take the gimmick out of the deck if you want, it will not ruin the gimmick.
Okkkk ....anyways before this thread gets closed.
To sum it all up, don't perform at school not worth the trouble. Focus on education!! Take advantage of performing outside of school.
-Rahat