Hi there! The idea was to put a price on your creation, not to get ad revenue from it. You will have to upload your game here on itch.io, but you can always choose the "pay what you want" model with a recommended price if you're hesitant on putting it for sale at a fixed price. If you ever feel like you were not successful and it's not worth selling, putting it for "free" is also possible so that you can show how far you've gone. No pressure about this, you'll figure this out at the end of the challenge depending on what you've done anyway.
I'm no marketing expert or anything, the idea here is to take the marketing side at least into consideration during the duration of the challenge, I explain this with more details here.
If you're scared, don't be! It's a challenge and there's nothing happening if you don't succeed. In any case, it'll be a great learning experience. Maybe try to find a team so that you don't make this alone?