You didn't mess up. Your therapist did. It's not therapeutic to say "if you don't believe in this I'm going to kick you out". It's not therapeutic to terminate a patient after three measely sessions because they haven't immediately leapt upon the therapist's kumbaya train.

Three sessions in your therapist should be showing you what she can do for you, explaining therapy in greater detail, and exploring the feelings you shared with her, not shaming you into feeling that it was a mistake to ever have spoken your mind.

I would skip the next session and find yourself a therapist who doesn't suck more than a tornado at tea time.