My teacher wants to take 2 unreasonable points off my midterm?

Today, i walked in 5 minutes after my bell, first period, and so did a couple other people ( not together) , because of the weather ( it was snowing ) . My teach told me, and another 3 people that he would take two points off my midterm & i cant afford to lose those two points. i want to send him an e-mail explaining why, i dont think this is fair. Or should i just get my mom to write the email? Either way, what should my mom or i , write ? can you give me some reasons? thankyou ! 10 points !