Making a button set is a good idea because it allows only one of the set to be in a selected state at any one time.
The problem is the individual variables are set to true When the state is selected, and never set to false if it is deselected. In more technical terms, you are incrementing, instead of counting. Incrementing is frequently a bad idea, because, as you have seen, it leads to inaccuracies if the learner clicks something twice, or changes their mind. Better is to count (or check) at the end. In your case, the trigger for Abi is changed to this:
That way, you save your energy until the learner is through fiddling around and has made a final decision. A quick check tells you what the decision is and you have to make only one change.
Another option would be to use only one variable, and set it to different values according to the last selected avatar. While that is a very serviceable idea, I don't recommend it in this case, because you have built a bunch of slides using all the different variables. It would be a lot of unnecessary work to change them all on each slide. That is why I recommend changing only the triggers on the choice slide, and letting your other slides continue as normal.
One thing I would recommend for next time. Put these triggers on the Master, instead of re-inventing them on each slide:
