That's the problem I had with it, too. It seems that the size of the finished blocks is 3". The star points are made from half-square triangles. I count 6 squares in one fourth of the star. So, that's 18" x 2= 36" for the entire star. That's a good size for the center of a quilt. You wouldn't want it any bigger than 45". It looks like this one is about 40" x 46".
There are 2 ways to enlarge a pattern
1) Add more borders.
2) Increase the size of the blocks.
You can do the first border suggested here, or even 2 borders, then set that on point (rotate so it looks like a diamond). So, 39-40" x square root of 2, will give you a new square measurement of 40 x 1.41 = 56.4". That would make it a good size for a double bed or for a queen size bed.
If you just want to continue with the squares, just keep adding borders till you get the size that you want.
If you want to increase the size of the finished squares to 4", make the first squares 5 3/8" (add 1.25" to finished size - but they added a little more). This will also require increased yardage - it should be 1.33 x more, but I would make the yardage 1.5x larger.