A little jump spot you can use to skip to the "ending" of the game so far.

Congratz. Now submit it to the leaderboard.

I would but I don't really want to be responsible for rules/moderating the games leaderboards. Is there another way to submit it?

If you don't want to request the game for the site yourself, you will have to wait until someone else does so. Although I don't know what are the chances for the game to be accepted with a 3-minutes run.

Seeing as Grounded is in Early Access and the developers expect a 2021 full release, plus the current best run (yours maybe?) is about 3 minutes, I doubt it'll be accepted currently. I also requested an Early Access game a couple months ago, and that game has half of its content available, making it around a 30-40 minute speedrun, but it was rejected. They just said to wait til the full game is released.