Help with a storyline

LEGO blocks are crafted with a fair amount of engineering and precision so trying to reproduce that effect will require similar.

I think the biggest hangup will be the bounding boxes of the bricks. If I select a brick, for example brick 2, you can see the bounding box includes a lot of empty space on the top and sides. Your drag-and-drop destination considers that space part of the image when figuring out how to place the draggable. Dragging brick 2 to a destination aligns it according to the bounding box, not the visible part of the image because Storyline cannot see the interior of the image nor make assumptions about how you want it to compensate.

I used the Crop function on the blue brick to better define the actual area of the brick and it now sits very nicely on its destination. I would recommend doing similar to the rest.

Additionally, you'll notice that bricks 3 and 4 are very differently sized. I checked all four and none of them are identical. That inconsistency helps break the illusion of the LEGO blocks you're going for because LEGO are very deliberate in sizes and dimensions. After each brick has been cropped, can I recommend left-clicking each brick and setting its dimensions manually in the Picture Tools menu at the top of the app.

Thirdly, the drag-and-drop feature seems to determine the depth/Z-order of draggables according to which object was last dragged. This means the "studs" of the blue brick below will always have a higher Z-order of the red brick higher on the canvas because I last touched the blue brick.

If I click on the red brick and move it just a little, it assumes a higher Z-order:

All this is to say that the exact LEGO effect you're looking for may not be easily accomplished. The only solid solution I can think of requires changing the Z-order of the objects using JavaScript, but that sounds like a lot of effort to me personally so it's not one I'd pursue.