I wouldn't, if I was you, let this situation be brushed under the carpet. Talk to the headteacher and if he appears reluctant to help, find a teacher with a senior role who would be willing to go with u to the head teacher. The worst mistake you can do is not doing anything.
I don't understand why the head teacher would choose to ignore it, given that the fact there's previous evidence, i.e. last years coursework. I think the last option would be to get ur parents/guardian involved.