Embarrassing Story! Accidental Ejaculation!?

Okay, well I am 14 years old and I am taking some summer school classes to be more advanced next year anyway, I have a desk in the very back corner and nobody can see me or what I'm doing so I started rubbing my pen*s through my shorts and I ca*e. I'm wearing white shorts and now I am walking around with a big stain on the front of my shorts! What do I tell people it is?