I love me a good TD game! Great work for your first game jam and I like the premise of the map spreading as the rounds go by.
However, I do wish that the map started in fullscreen and as it grew slowly zoomed out. The small square in the top left corner of the screen is a little hard to navigate.
What do each of the towers do? It was tough to understand which towers did what and how to strategize against enemies.
Did you have a specific reason for starting with $125? Nothing in the game was worth that $5 and the number of towers I could place couldn't reliably defeat enemies. So either more cash, weaker enemies, or more powerful towers would have been helpful.
Overall, I think you have a very solid start and with a little polishing could be a super fun TD!