You don't need any tricks to do this: just use the data in the natural way
+---+------------+---------+---------+
| | A | B | C |
+---+------------+---------+---------+
| 1 | difficulty | samples | results |
| 2 | 0 | 1 | 3 |
| 3 | 1 | 1 | 3 |
| 4 | 2 | 1 | 3 |
| 5 | 3 | 1 | 3 |
| 6 | 4 | 1 | 3 |
| 7 | 5 | 1 | 3 |
+---+------------+---------+---------+
Select the range A1:C7, go to Insert > Chart, switch to "Chart types" tab and pick Scatter. Here's what I get:

(If the data is arranged as you have it, with separate rows for separate series, it still works the same).
A potential pitfall: if on the "Recommendations" tab (shown by default) you click a scatter-looking plot "samples vs. difficulty", this will yield the bad chart in your post. Just ignore the "Recommendations" tab.
