Hi, welcome to the forum and congrats on your first mix!
From a balance point of view, some elements work really well e.g. guitars in general, bass, kick and vox all seem to compliment each-other. Well done on that as these are crucial elements of mix building.
Elements that seem not quite so balanced are the piano levels being a bit hot, especially in the bridge and the snare tone and level which is very thin, papery and low.
The biggest problem you have are your levels......A master level of -6.5 LUFS and a dynamic range of only 5. That's 5-6 LUFS louder than spotify/apple music streams at so you're leaving 6dB of dynamic range in the tank for no good reason...
my biggest suggestions for you are;
1. Educate yourself on how to gain stage your individual tracks in your DAW so that your peak mix buss levels are around -5dBFS MAX with your RMS levels around -15dBFS. You can then boost your mix buss level after you have finished your mix.
2. How/when and IF to use compression.
3. How to set final master levels including how to use a LIMITER properly. I'd recommend levels of around -12dBFS RMS/-12 LUFS....maybe up to -10 for some genres.
4. Get to grips with the units of measurement e.g. dBFS, dBVU, LUFS, RMS. They are all different and engineers bandy them about alot (like i have
).
All this is readily available online but a range of answers exist (Mike's book "Mixing Secrets" is excellent). Good luck.
Hope this helps
Cheers, Simon