Jen
Sorry to hear that. Wanting to keep yourself chaste is a really big commitment, and there are bound to be moments when you really want to quit and get it off. Of course once all possibilities of self-pleasuring are eliminated, that will happen more often. And apart from that there is the inconvenience of bathroom visits, more limited positions for sleeping, etc. That is why you need a keyholder, to prevent you from giving in at those moments, and help you achieve your long-term goal.
I guess you are wearing the belt often enough now to get a better idea of that commitment, and I hope that helps you in figuring out if your goal is actually worth it. And like I wrote before, I don't think you can reach that goal unless you also stay belted outside the house, which was a big no from you until now. It also seems likely that you will manage to get a breast orgasm sooner or later, so you will have to decide whether you are still keeping yourself chaste if you do that. (The opinions on that differ.)
Of course you shouldn't just give up if you have a bad day, so I would advice you to start taking your doubts/resistance seriously if they continue for a number of days, say a week. Since your parents seem to be working with you now, I think it might be good if you share this feeling with them: just that you are having a bad day. Of course you still have options to take a break as well, as long as you catch up later, or forego some driving practice sessions. You have also been thinking of only keeping this up until you have your license, but I'm sure after that your parents will be able to find something else that is tempting enough to keep going, so if you are sure you are no longer committed to the goal of keeping yourself chaste for Mr. Right, waiting longer will probably only make it harder to quit.
How is this average of 12 hours per day working out for you: are you regularly warned that you don't make enough hours? And how many nights per week are you doing now? Do you sleep (almost) as well as without a belt now? Is your self-pleasuring less now that the moments that you have access are getting fewer, and you can't do it anymore whenever you feel the urge?