You can use the left, right, and up arrow keys to move the character. The only thing the up arrow key does is make your character jump. I cannot change anything until the judging period is over. It works for me in Chrome. The game page scrolls in Microsoft Edge until I press F7 to turn off caret browsing before I run the game. It now works in Microsoft Edge. Sometimes, the issue is a browser issue. Let me know if you still have trouble.
Updated: I have added a full-screen button as an option from itch.io. You can try that too.