It sounds like you are feeling so disappointed in yourself that you are contemplating running away. It's very normal to want to run away from your problems but running away won't solve anything. You'll just increase the amount of problems that you have versus having the opportunity to resolve them. Know that being on the run is never a safe situation.
We would encourage you to talk to your parents about your report card before they hear about it elsewhere. Please consider reaching out to a trusted adult such as a aunt, uncle, school counselor, teacher, coach, or minster. The goal should be to have an adult who can support you in preparing to talk to your parents or assisting you in doing so. Be assured that there is help available to you through your school to help you with your classes. Please consider getting into counseling if you continue to struggle with your classes or emotional pain. It may help you to talk to a counselor at a hotline. Know that there is help out there for you and you are not alone.
Boys Town National Hotline 1-800-448-3000, www.yourlifeyourvoice.org