Interesting song... yes, it could be louder... try a different limiter perhaps? And I feel the piano could be a bit brighter and use a bit more reverb (maybe some EQ in the mid frequencies could help too)? Also the strings' velocities could be varied a bit... [humanize?] But I love the piano melody and the synths change the piece quite a bit! I can see you're a Logic Pro X user just like me, good to see that (guitar gave it away)! Nice stuff!