You'll need to complete a lot more shops to increase your self-assign limit. The percentage increase for each shop decreases as you reach the level (~3% for Level 2, ~2% for Level 3, ~1% for Level 4, ~0.5% for Level 5; Based off shops that receive 20 points, which seems to be pretty standard). I'm at Level 5 and my self-assign limit is 5. The MSC can also implement their own self-assign limit for their shops. There's a grocery compliance shop that at some point I was able to self-assign as many as I wanted. I'm not sure if that was based on the level I reached for the grocery store badge or if the MSC decided to get rid of the self-assign limit for me.