I have explained the necessary tweaking to quiz slide design in a rather old post but the principle is still valid:
Question Question Slides in Captivate - Captivate blog
The quiz slide is pausing at 1,5secs, I see that you didn't change that pause, why do you have such a long duration for that slide?
The normal design has a two-step Submit process: first the default shapes or captions appear as feedback, then (if it is the last attempt) the user needs a second action: to click on the slide or press Y. Only at that moment the playhead is released and the actions defined as Success/Last Attempt will be executed.
I see that you still have the 'correct' message checked off. That means that you still have two steps in the process. You have to uncheck that one as well to get rid of the first step of the Submit process. Then you'll be able to use the actions (Success/Last Attempt) to show the custom feedback group. But at that moment the playhead is releassed, which means you'll have to use another pausing point to prevent that the playhead continues through the intactive part of the quiz slide and proceed to the next slide. You can put a Next shape button (other interactive objects are not possible) with a timeline that starts 0,1sec after the present pausing point, and give it another pausing point later on. That shape button will then execute the action 'Go to Next Slide' which is the default choice for any simple action.