Need a good reason !

Me 17M have bunked my classes for 6 days straight well hanging out with my gf 18F and now my mom called the sir to ask how am I doing in classes and the sir was like well he hasn’t came in the class since a week while I bunked telling my parents I go to tution. Well I got scolded by my parents for this but now I need to give an explanation to the teacher and I need a solid reason so as to why there was a need to bunk classes