Am I being paranoid or is my boss trying to demote me?

My boss manages a classroom. I help her around and manage her class when she is away. Recently she adds a colleague of mine to the class because it has got too large. She is younger than me but has been around my workplace for longer than me.

Recently I start to notice that my boss gives work to my colleague when she is away. She normally gave that kind of work to me before the colleague stepped in. She still gives me work, but I have a feeling that the colleague is getting more work than me. Just recently I heard from my colleague that my boss asked her to come down to her class to take over her place for the day, and the time for that task is actually my fixed time for that class. It was as if the boss didn’t remember I was already there for her.

I feel kind of afraid right now. I don’t know if my boss is slowly trying to replace me with my colleague and move me to a lower position. I have a lot of questions if that’s the case. What did I do wrong? Does my boss hate me now? Am I going to lose my job? Another colleague told me that she may just be dividing work equally between us, but I feel that she is giving me less responsibility than my colleague.