Considering the constraints, it's okay. The gameplay is really simple and the poo theming doesn't really do it for me. Perhaps you could add obstacles like poo that shoots back so you have to dodge their shots before firing or poo you can't shoot, any obstacle would be appreciated to make the gameplay more engaging since otherwise you can just constantly fire and move side to side and as long as you can fire super fast you'd be able to make it far. If anything, I wish you luck in your game dev journey, we gotta start somewhere and this is a pretty good start.