How do you remove deep scratches on MacBook air?

Outside of replacing the LCD assembly, there’s nothing you can do to try and fix it. You can blend it in on the plastic machines with a plastic polish, but it still doesn’t completely remove the damage done to the system. Once the damage is done on aluminum, that’s it - you can’t blend the damage in.

Unless this is school issued and your district charges for petty damage like this when it affects absolutely nothing (or charges more then the true cost, which happens), I would leave it alone.

If it’s yours and it really bothers you to see it happen again, get a case that covers the system to prevent another accident on a site like eBay. The super cheap ones all come from China, which takes it’s time to ship to the US. If waiting is out, check Amazon for a Prime shipping case - these are usually sold by Amazon or FBA.