Isn't it impossible to lose points until your rank is high enough? The official rules said so:
https://i.imgur.com/sYaDyID.png
I'm a huge fan of Mahjong, but I understand that the length of the game can be intimidating to new players. You must be very lucky to complete a game in 30 minutes. In my experience, on average, one game lasts about 50-60 minutes. The last game I played was completed in 90 minutes.
I think the solution is to let the players choose between full match and half match. The caveat is playing a half match only gives/takes half the points of a full match.