This could have occurred for a couple of reasons. First, you’ll want to think back about whether you may have inadvertently used any avoidance strategies or safety behaviours while you were doing the exercise. Were you trying to distract yourself, avoiding looking around, looking at your phone, or listening to music? If so, try the exposure again, but without any of these avoidance behaviours.
If that wasn’t the case, it might have been that you over-estimated how much distress you might experience in the situation. Sometimes you’ll find that situations you ranked as potentially distressing, really aren’t as bad you thought, while others are more difficult. If you over-estimated your distress level, that’s OK, just move on to the next item on your hierarchy.