I bought the 2d pixel art course but if my design sense is not the best can I still make good designs for the game I want to make?
While the pixel art courses are designed to get you comfortable from a beginner skill-level. Art is a skill that is built over time, so while you might not be able to get things to look exactly how you want them, with continually practice and study you’ll be able to work your way up to what you want.