Thanks for your feedback! I already implemented a little buffer zone around the items so picking up is easier, but it seems it still could be larger.
Considering placement, the items are actually placed on a grid, but there's an additional offset to hide that. The grid is just to make it easier to prevent items overlapping. Don't mind the scoring too much (as in "I want perfect score") because I had something in mind for the contracts like "reach at least 50 accuracy to pass". Another option instead of showing numbers would be having categories like "+++", "++", "+" and so on, that would hide the imperfection a bit. Though I personally like the sensitivity.