What would you tell your teacher if she called you while you were skipping class?

So, I took a class for extra credit, and also because it sounded pretty interesting as well. I can’t say that I’ve regretted being in it, but with my schedule and grade 12 year, it feels like all the pressure is on me. For a while now, my friend and I (both enrolled for that class) have been feeling it to be quite tiresome. It goes on for 3 hours straight, right after school! (only twice a week though)

Yesterday was the 2nd time that we decided to skip her class. The first time, we had called in sick ourselves, but this time we didn’t care to. I was at the mall when I got a phone call on my cell, and I don’t have caller ID. When I picked up, it was my teacher. “Hello ________, will you guys be coming into class today?”
Me: “Ummm…... O_O… Hold on!”

And then I put her on hold to tell my friend who had called. I had no idea what to say. I never had a teacher CALL me before. It was strange… I took too long and to my relief, she hung up on me.

What should I have said to her? Just “no I will not”? I wouldn’t know how to reply if she asked why…