Sounds like you did a number on yourself, getting to worrying about when therapy might end and what it will/will not be like, your getting better, etc. and so grabbed hold of a security blanket?

Feelings don't "go away" anymore than they can "get stuffed" Feelings can be helpful, like dreams, to tell you want is going on with you in relation to your life and other people. If you have a recurring dream, it is a good bet that there's a message from your unconscious to you that you aren't paying attention to? Pay attention, and the need for that message/the recurring dream goes away?

I had to do the work, toward the end of therapy, to not get ahead of myself, to not anticipate what was going to happen next week, month, session after next, etc.; you are doing certain work now and that's what you need to concentrate on, any other worries/speculative thought when you are in 10th grade about, "OMG, I have to graduate high school in only 2 years!" is no different that a nasty day dream, the daytime equivalent to a nightmare. Focus on the problems, right now, what you are working on, right now, and you won't have to worry, you'll be too engaged in doing what needs doing right in front of you.

There's nothing wrong with you for having a nightmare or day mare (thinking "old" thoughts you thought you had dealt with). They are there to help you but in and of themselves, they aren't "true". There are no literal monsters in the closet, it's symbolism for something else.