I'm failing grade 8?!

School can be very hard sometimes.  I would try talking to teachers of some of the class(es) you are having problems with and see if they will provide you with some extra help.  Many teachers want to see students be successful and are willing to give them the extra help if they see willingness.

Study better and harder.  Ask teachers for better ways to study.  Learn how you learn best as everyone isn't the same.  Sometimes it isn't about studying harder, it's about studying wiser.