Fun concept, but there are some implementation details that hold it back. Quite often I was just roaming around, not encountering anything, to only see an enemy 10 times my size. Most of the time those were the only circles I found, requiring me to shoot a dozen times to gain a little bit of size. Never was I bigger then a spawning circle, so I could actually compete with the larger shapes. There is good variety in enemies, but before you have substantial mass, I cannot deal with stars, and rectangles and triangles don't help me gain size. So I never reached a position where I could actually compete with enemies. It could also be clearer when you are bigger or smaller then an enemy. Comparing circle to square sizes is not so intuitive, and it is an instant death if you are wrong. The background also behaved weirdly when hitting an enemy (circles and rectangles). With each hit the background got smaller, persisting between resets, until randomly getting larger in equal steps.
I hope you learned a lot from you first game (like I had all those years ago), and I wish you good luck on any further endeavours.