This is very fun to listen to!!! I like how expressive the saxophone sounds at times, and the choir adds a lot of excitement.
I think much work can be done to make this sound more realistic and even livelier. I would add more early reflections reverb on most instruments. This helps add a room sound to the samples rather than adding a tail. Adding a tail to a dry sample won't sound nearly as good, and it won't blend well with samples that have a baked in room sound. I think the song could benefit from more high end percussion; there already is some but it's not prominent enough imo. This can help the track sound more open and energetic. The clap sounds overly widened; imagine you're in an audience watching this performance live, and think about where the clapping is coming from and how your brain would perceive it spatially. I think the instruments can be spread out more over the stereo field; you might find the plugin Panagement useful.
I believe some additional EQing could make the mix a bit better. The bass region of the bass instrument can be cleaned up a bit, and the low-mids of the ukelele can be cut slightly for a cleaner sound. I think the high end of the claps, vocals, ukelele, and saxophone can be boosted to liven the mix.
This is great work. Good luck in the contest!