That's how it initially was. But I have now made it so that, as you say, it first checks to see if it's a multiple of 7. If it's a multiple of both 7 and 3 (regardless of whether or not you have played it before), then you will no longer be penalized.
I think I understand why you decided to do that, but it might be worth an explanation modification. I tested my understanding of the rules by trying 21, and was surprised. Not that it's a big deal!
