Hi Paula,
If you want to list them in one listing, you have to state clearly that you only have one of each. It's probably safest to list it as qty. 1, then the sizes in variations. If you list qty 5, then you have to go on an delete the size right away that has sold, when it relists.
BUT if you copy and list each seperately, like you have in many cases in your shop, then it will show up more. You pay 20 cents for each listing, but you would pay the same if your item sells and you relist it with the new sizes.