Neat little game! I like the stats you have, and the general loop is a good place to start. A few ideas that can spruce things up for relatively little development time:
1. Make the player invincible for a bit after they get hit. It's really easy to take 3 or 4 hits in a row when there's a big mob attacking you, which can feel unfair.
2. Adding different enemy types by tweaking variables (i.e. slower enemies with more health) can add a lot of variety quickly. It also makes the decisions of which upgrades to take have more weight. With just one enemy type, the damage increase is effectively useless until it causes them to be killed in one less hit, making the round's upgrade feel a little less exciting than it could be.
3. This is a minor but important detail, currently the player can go into the sides and be completely hidden from view because of the border, so making sure they can see themselves is a good quality of life change.
Great work, congrats on completing your first jam!!