You shall be his people, and he shall be your god.
For real though, this is such a strong entry. I love the customizer, I love the art, I love the way everything swims. From what I've seen this is the most complete game I've seen. You have roughly 42, 504 combinations (though they are technically infinite).
Since you treated me so kindly, I return the favor by saying this. I really really wish that the placement was more consistent. I don't know what causes it, and I really tried to look from an outside perspective, but sometimes I can place items, and other times I can't. I also wish that placement could happen on more than just the starting body. I think it's probably for collision purposes, but at least being able to scale the starting body would add a lot of options.
I also would like to see a few more generic parts. It looks like the ones you have here are kinda meant for a specific creature. Maybe it's a scope limitation, but having some more utilitarian parts even like simple squares and triangles and such could go a long way here. In a similar point, having the mirroring be a toggle would make this feel like a perfect customizer.
All around, I cannot believe that this only took you two weeks. This is an incredibly impressive project