All I could do was shake my head at this. I am 5'8 155, I love to fight. But there are certain fights you just shouldn't do and you my friend are going to get worked. like yeah yeah people are saying 'move around quickness keep your dukes up' which is all well and good. But you may fail to realize the actual strength gap between you two. Even if he has no idea what he is doing and is just throwing fat hooks and you try and block them it will still be a heavy hit. Your little pencil arms wont do much blocking against that type of force.
You will more than likely lose the fuck out of this fight,but I have fought a kid that was about 6'1 220 and kicked the shit out of him. Granted it wasn't boxing and it was an actual fight and I was a wrestler for quite some time. I took him out with a right hook to the jaw followed by a left straight to the nose.
Try and get him in the nose and jaw. No matter how big a dude is getting punched in the nose blurs your vision with tears, and you could be andre the giant and have a glass jaw and gt taken the fuck out.
Good luck, I want to say I have faith in you coming out on top, but I don't.
Don't get yourself hurt, and don't feel obligated to box this dude, it's okay to walk away from it.