Well done for a first jam, and especially after missing out on over half the development time! I enjoyed playing this quite a lot. Was very quick to build a max tier sword unpunished, reached round 9 then decided to see what happens when I died. I got ded, deconstructed, and lego'd. Did you happen to be inspired by Cursorblade, a very similar game?
Also, I know "Unstable Concoction" as a tower from Bloons TD 6:
Is this a reference or a coincidence?
What I might improve: progression/some form of ability system.