Not bad for a first song sharing, in fact, it is much better than my first one, so keep working on this and you will see how it will all come together. Some things to think about when mastering music. Equalization, Reverb, Dynamics, Stereo Imaging, Harmonic Excitement, Limiting Maximization, Post Equalization, Noise Gating and Dithering. All are very important to come up with a good final mix with a full quality sound. Again, very nice start to something much bigger and better. Keep up the good work and best advice I can give you is to read and learn all you can.
Peace and blessings, John