From a game jam persepective i think its a very good submission and i can't really give suggestions since it would be too picky.
But from one game dev to another i can give you my personal view as a gamer of it in general so you might get another feeling for the future.
The balancing is a bit too player-sided for my taste, i don't think you can really loose a card if you don't do an oopsy. With it you can focus full on getting more money and upgrading your current cards to not loose cards even more. With it comes that "buying new cards" and "new cards level" become an empty button.
(but i know you might have planned some things that didn't made it into the game to balance that out)
Still, Numbers go up = fun. Simple as that. Smooth animations and controls lets you stay in the flow.
In conclusion: Balancing - especially in a set time window - is hard and needs much experience. Atleast i never get the balancing right the first time and need some patches :D
Hope you can use these insights from a players perspective. Keep up the good work <3