For some comparison of difficulty, there's an old game called Squares which is very similar to yours. It does a good job of ramping the difficulty up pretty fast, but it allows the game have fun short gameplay loops because of the extra gameplay mechanics (ie, you are not just moving but collecting squares too).
Gameplay Video: https://youtu.be/n8nRCyjCy_Y
Apparently you can still play it online at: https://www.albinoblacksheep.com/games/squares2