This is a decent map! I found it pretty fun, but I believe there are a few things you could improve on.
The theme should be good, since while there are a lot of maps of instruments I don't believe there is a map of a saxophone yet. Theme should be good!
The build is pretty solid! I'm not the best builder myself, so my standards for a good build are pretty low. I believe that this is good, but I don't know what the map judges think. I'm sure it's good enough!
I believe that the biggest problem is the parkour. In my opinion it is too difficult for the Medium difficulty you are going for. I recommend you to nerf the course, since there are quite a lot of tricky jumps that I believe do not fit in a Medium map!
The second problem with the parkour that I can think of is it's repetitiveness. While I don't think it is an issue, the map is quite crowded with ladder jumps, which might hinder the chance of your map being accepted. They fit the aesthetic of your course though, so I can understand why there are a lot of ladder jumps!
The third problem that I believe might have a slight effect is how much the parkour of your course hugs walls. I personally didn't find this an issue, but I know that some people might! The map is quite hard to make "not wall huggy" however, so I don't know if that can be counted as a big problem!
Remember that my opinion doesn't affect the judging results! I try to give information that increases the chance of maps being accepted and their enjoyability! You do not have to make any of these changes I suggest you to make!
Good luck! :)
EDIT: The map has been nerfed from when I tested it, and the ladders have been reduced a little bit, but I personally still feel like it could be nerfed more to better fit the Medium difficulty! Map Judges have the power to decide it however!