I don't understand, why I just got my ass chewed for giving extra credit?

I'm a student teacher, and the students in my World History class are taking their final right now. <br><br>One of my students is in danger of failing, she's a very sweet kid, and I don't want to see her hurt by this on a minor assignment that's not that big of a deal. <br><br>I wanted to give her extra credit for a project she did earlier in the semester that showed hard work and dedication, but the principal absolutely flipped her lid at me and told me that it's not my place to do that. <br><br>I don't get it, I'm trying to be the cool teacher. How will this hurt anyone?