Sorry to hear about this.
Your son is going through a typical adolescent phase - finding his place in the family, and the world - and often teenagers overcomepnsate for their insecurity by being overly brash and aggressive. They are hyper-senstivie to any percevied slight, and can loose their tempers in an instant.
These problems are exacerbated by your son's physical size, and i am sure he does not inted to frighten you, and would be upse to hear that he does.
The way around it is to make sure you reassure him that you love him - he's never too big for a cuddle from his mum! - and that everything you do and say is based on keeping him safe and happy.
Find a quiet time to tell him that his tempers upsets you, but don;t say he frightens you - merely that he makes you sad, and you know he doesn;t mean to, but must learn to curb his temper.
You must maintain your status at all times, but hopefully without confrontation. If it does escalate, remain calm, and remind him of your status, and his, and the way they relate to each oither.
Have a word with his teachers and explain the situation, and ask them to be sure to enforce a sense of discipline and respect which is so important to boysa t this stage.
This is a phase, and it does pass - so don't worry unduly.
Good luck