This is a fun little game. One thing I noticed is that is feels a bit janky when going out one side of the screen ans coming back in from the other side. I think this is due to the circle not being rendered when overlaping. To solve this you could make a 3x3 grid of circles that move along with the player, just spaced by the height and width of the screen.
Also, if you reach critical mass, you could implore into a black hole and become a galaxy, like a level 2