It's happened to me too and it is frustrating, even when I play as one of my healers with the shorter wait time. People are so disrespectful of others' time.

Short story. I queued up for what I thought was Amp Township (I was really tired and not paying attention) but quickly realized I had chosen wrong when the Amp Keep cut scene began. Even though I had no desire to do Amp Keep, I didn't ditch. I stayed through the whole instance.