Rescinded from Williams College?

I was accepted to Williams College regular decision, which is the number 1 liberal arts college in the U.S. They have high academic standards. I got an A in AP Literature first semester, and a C second semester. This is because im going A E for third and fourth quarter. I originally had an A for the last quarter, but a friend (no longer my friend) plagarized three of my essays from taking it from my essays folder. My teacher will give us both Es for being involved, and my pleas have not been helpful in getting leniency. I am worried that Williams College will send me a letter in the summer asking me to explain this drop in grade, and in that case I will have to tell them about the situation. I am worried that since this situation falls under the plagarism category, this will raise a red flag and get me rescinded? What are your thoughts?