Who's to say whats "adequate" for a high school student? There are adults who've paid for courses that have trouble producing similar quality work. Question is, are you happy with it and did it help you grow as an artist?

My only real crit with the winter scene is that there seems to be some gamma issues, everything is quite washed out. That's one of the hurdles created by using the mr physical sky and I ended up writing a script to help me deal with that.

The outer space image seems to have a bit too much sharpening applied. I think it could use some subtle planetary glow/halo, right now the two masses seem pasted onto the starscape background.

It never hurts to step up your game, nah I'm lying, it's probably going to be frustrating and you're going to want to punch your monitor at some point but that's part of the fun!