I see you mentioned that this is your first Unity game, and that you were keeping the scope small to ensure a finished project in the end! Joining jams as a learning experience and keeping the scope realistic is both smart and commendable!
The game itself is quite simple, picking cards and hoping that you've chosen well and will overcome the random card the enemy draws. My first attempt was a draw every turn, and my second attempt I won! Gameplay-wise, it feels very luck of the draw currently. It's hard to strategize beyond throwing down your best cards and hoping for good luck. The "Dragon" card seems the least useful in my games, as it can beat any card, but will always be defeated at the same time. The interface is functional, but could use a little pizazz. SFX and/or music could go a long way to enhance the experience too.
Graphically, things are fairly simple. It'd be nice to have more UI, backgrounds, etc. The character art is nice though, and gives a glimpse at what this might look like if the game was expanded and polished.
Overall, it does feel like a prototype... but you've learned new skills and have a final product to show for it, so that's a big win. Keep at it!