If the light was on right after you turned your car on, it's most likely that someone slashed your tire. Think about it, what are the chances that your tire is a little low and then while driving for only 10 minutes a gash appears on the side of your tire.
It looks like someone just took their own car key and stabbed your tire. Are you sure you didn't piss anyone off recently? Or maybe you were showing off that fact that you have a brand new Sonic to your friends and someone who doesn't really like you overheard. I mean you are at a school with a bunch of teenagers, they have nothing to loose by slashing your tires.
As for not noticed the flat, I'm assuming everyone at your school basically gets out at the same time. That someone could have seen your car, slashed that tire, and then a few minutes later you go in and the tire isn't fully deflated. Then is deflates a lot more during those 10 minutes of driving.
I'm 18 years old too, so I can see how noticing the light and not checking your car can easily happen. Think about it, your with your friend in your car, you notice the light. Maybe you don't want to check your car because you don't want your friend to be like "what are you doing? let's just go." Thinking, "well I'll just check it when I get home, no big deal." Also it's a new car and probably your first new car, like-wise is mine. You don't really expect the tires to already be messed up.
I don't know, just trying to look at this situation from a closer perspective. At the age of 18 this could easily escalate in to a major problem