Drag and drop with multiple same answers

Hi! I'm having an issue with a drag and drop activity.

So this question has three drags that are the same and can therefore go to any of three drop targets. I used this tutorial to setup my initial structure - https://www.youtube.com/watch?v=07aWCa6T5pc&feature=youtu.be - but now have another issue.

Since I'm not using the built in drag and drop activity setup I can't specify that I only want one drag item per drop target, so they end up stacking together. I tried adding triggers to hide the drop targets when something is dropped on top, but that makes it so the user can't rearrange the answers if they change their mind on their answers because the drop targets are then hidden. Currently the activity itself is housed on it's own layer so when the user hits the "try again" button it can be reset, but that doesn't help if the user is in the middle of answering and wants to change their placements before they submit the activity.

Is there a way to make a drag and drop where multiple targets can be correct, but multiple drags cannot be stacked onto one drop target, AND the user can rearrange their answers? The file is attached, thank you in advance.