Keycaps are measured in unit size, where the alpha keys are 1 unit. The bottom row total is 15 units, and there are two common configurations:
1.25 | 1.25 | 1.25 | 6.25 | 1.25 | 1.25 | 1.25 | 1.25
1.5 | 1 | 1.5 | 7 | 1.5 | 1 1.5
You bought the first and you need the second. As codyeatworld said, these care called tsangan kits and can sometimes be bought separately, so you shouldn't have to buy an entire set.