My guess is you have two question groups with your quiz and one of the two has all of the questions selected. Or perhaps all of the questions were selected accidentally. Attached is a screenshot showing two question groups within a quiz, one with a link to a question bank (3 questions selected) and the other with those same questions included in the group with all 8 selected. Luckily changing the number of questions selected is as easy as editing the question group.
Two question groups in one quiz
I'm going to assume my response offers a solution and mark it as such. If that isn't it, please reply.