I don’t entirely know how making a jam works, so I sadly cant assist much. But looking at the jam page, there are a few things you can do to make it look better and more professional:
1. Use a different font, the font used currently is a bit generic.
2. Add some parallax to the background
3. Instead of explaining the important stuff like rules, themes, etc in basic text, make seperate images for them in photoshop or another software stylized to the colors/font the jam is using explaining the important things, then paste them into your jam description.
4. Overall, give the page more life; it feels a little dead right now. It could be a bit more vibrant
I wish you luck on promoting the game jam, good luck :D