If it's printing smaller than expected, you probably have to reload the pattern into the Rapid Resizer and make sure to crop it tightly. Specifically, in Step 3, the red box should tightly fit the area that you want to resize - not the whole page, but the pattern in it.

If you're trying to change the proportions (how wide your pattern is compared to how tall), make sure to uncheck the "Lock Proportion" box before entering the size you want.