Right scaling solution
As far as I know there is no tool for fitting the created UV layout to the whole square. But you can do this: [In the UV-Editor]
- select all verticies A
- scale your vertecies on the x-Axis by the factor 1.45454545. S + X +
1.45454545
- pack the islands Ctrl + P (We do this to center the UV-layout. This makes it independent of where your scaling pivot point was)
- if you want, you can choose a margin, so that your map isn't exactly in the corners (F6, then enter something like .333 in the margin field)
Your map should be aligned centered now with no space of the light gray square except the margin left.
Why is the factor 1.45454545?
When you look at the screenshot you can count that 5.5 of 8 (large) squares of the x-Axis grid are filled. So $\frac{5.5} 8 = \frac{11}{16}$. If you want to scale them, so they fit 8 of 8 squares, $\frac 8 8 = \frac 1 1 = 1$, you have to multiply by the inverse, namely $(\frac{11}{16})^{-1} = \frac{16}{11} = 1.\overline{45}$, because $\frac{11}{16}\cdot\frac{16}{11} = 1$.