I failed a major school project and hid it from my parents and they still don't know
What was the reason why you decided to hide the grade from your parents?
My dad was rude to me when I tried to explain to him what happened.
While it may be ok at first, it is ultimately a bad idea to conceal how your doing in school from your parents. They are going to find out at one point anyway, so you are better off being up front about it. You may even get into more trouble if they find out at a later date instead of right away.
I can pay for myself until I go to college.
Don't you think your parents just want you to do your best? So hiding things from them all the time won't let them understand you and what you need to improve on. How about to always be upfront with them and ask how they can help, instead of hiding it all?