Some things to note:
-You gots to pan your instruments, period.
Since everything is falling in the middle, when all the instruments get together, it sounds pretty muddy, and I could barely distinguish the strings when they made their instruments. Just shift things a little bit to the left here and to the right a smidge, and this problem is solved.
-Use a bit of dynamics
This ties into the first point, in that every instrument is playing at the same volume at all times. This makes things again, hard to distinguish and muddies up the composition. Also, with not dynamics, parts of the piece feel a little bit lifeless.
-Strings need a bit of fine-tuning
For the most part, they're all right, and this is a note for FUTURE compositions. In the future, try to shy away from using the strings like block chords. Not that this is a bad thing, but I say let them live a little bit as instruments of their own. As well, in this composition the low block chords sound really muddy and hard to recognize, so now how to balance things out. I don't mean to sound like this is a crappy piece; it's not, and it's likable, but I think it was hastily released.
Mainly, the main thing this needs is balance and mastering. Fixing all the small problems so this can be a better piece as a whole. You said this piece took a day to fix; well, it takes far less than a day to address the problems I listed (minor edits at most). Hope this helps.