That's the intended behavior, it's like the ship where you hold to go up and release to fly down. Also, you should get Geometry Dash, it's only a couple dollars and will give you hours upon hours of playtime.
You shouldn't, I'm pretty sure the level data is stored somewhere else. I accidentally deleted my 3dash but when I reinstalled my levels were all there.
Edit: Your levels are completely safe. They ARE stored somewhere else.