I regret to inform you that your map is being rejected.
The theme is original, well done.
The build is a concern. The outside of your build is very plain (this does count a lot.) Overall, there's too much stone brick throughout, and the cylinder shape doesn't really make sense. To improve this, you should fix the shaping and maybe add some other types of details (vents have been suggested on the outside.) On the inside, the slime could use more detail (it's intended to be pretty "spooky" but feels underwhelming at present.)
The parkour has some decent variation, so well done there. However, the general path of the parkour is a problem. Most of the parkour is floating (meaning unattached to the main build.) Floating parkour is okay in moderation, but here it takes away from your build and makes the inside look messy. The difficulty is also a bit inconsistent for your difficulty. Overall, it could use an overhaul in favor of a better path.
Thank you for submitting this map, I would love to see more submissions from you!