Honestly, I think you should talk to your parents. I understand your need for independence, but frankly, it seems that you have tried solving it but failed miserably. Tell your parents that every payday, they have to ask you for $300. Then they can put it into an account that you have no access to. This way, you will have no opportunity to spend that $300 or have access to it later.
Also, consider looking into RESP. It is usually started much earlier, but I don't think there is an age limit as long as you still have not graduated high school.
Also, consider looking into RESP. It is usually started much earlier, but I don't think there is an age limit as long as you still have not graduated high school.