Yes, restoring it, the way, but you will still get suspended because you won't have the school apps you need. Like I said, you can erase the crime evidence, but that you are guilty is not erasable. Go to the office and come clean. There is no scenario in this where you get to have a free pass.
When IT/school administrator asks why you restored it, you might lie and say it was causing an issue. That might work initially, but after further investigation of the device they'll see it is working fine and you lied. Which will prompt further inquiry. You might say it solved the issue. And then they will say show us the previous back up and you know what? That is the evidence. Deleting it is not an option as it'll just get you into more trouble. Come clean... Go and take your punishment like a man.
Also, installous leaves a trail behind, hidden or not. Trust me, the IT guys will know and report the issue with your school and you will get punished. Sooner or later you will. So I suggest you just come clean and get it over with. If you wait until there is a holiday coming over or summer it'll be worse as you may have to do detention in summer or holiday. Get it over now.