Well done, especially for a first jam! I like the concept, sort of a top down tower defense. There's a bit of cool stuff with choice, like how you can choose to wait for the raft and save wood or just build yourself across the river to get where you need to be faster. Game looks cute too and sounds great, I like your overworld theme a lot.
One thing I would say about clarity is that I got the objective once I read below the game, but it was unclear before doing that. Something to get that across to the player before the core gets broken into would be good. Otherwise, awesome job.