Thanks for your detailed reply.
I actually didn't know I could change the images, thank you :)
For the platforms, I intentionally made them this. I thought it would make up a bit of a difficulty. I will work on that and think about your fix for that. Sounds interesting!
As for the spring level, I've encountered this problem too. I think this is because of half slabs. The springs spawn at the lowest point of each tile, so if they are placed onto half slabs, they spawn under the ground. For that, you can place the springs in the air, they are gonna fall on the ground! That's one thing I gotta fix.
Also, after the spring level, there is one last level with spikes.
Planned on adding other items for it to get fun :)
Again, thank you, have a great day :)