The best way to make a first game for a beginner programmer?

I am in high school now, and I plan on going to school for game development, eventually becoming a programmer specifically for games. I was wondering what the best route would be for me to take when making one of my first games.

I know a fair bit of c++ and python (classes, pointers, etc. but not much of the advanced stuff), and I'm getting the hang of using c# for Unity.

My question is if I should use Unity (or some other game engine like Gamemaker) to make my first simple games, or program them from scratch using SDL2 (or similar). I have tried to start making things a ton of different ways, and I need to follow through and make a full game using one way or another. Any advice would be greatly appreciated.