You can also try going up a needle size or two. But since it is supposed to be bulky weight, you will likely have to use double strands of it or just resize it by adding more stitches and having more rows too.
The thing about double-stranding is that it takes way more yarn.
First of all, I think you should knit another gauge swatch. It should be larger than 4 inches square. When you've finished it, steam it or wash it gently and let it dry. Then mark off 4 inches of stitches across a row and count the number of stitches. You'll get a more accurate measurement than when you measure the swatch edge to edge.
When you're subbing yarns of a different gauge, you want to be very precise about these things.
Then you can follow the instructions for a larger size, but you will probably have to do some fiddling with the frequency of decreases/increases if there's any of that kind of shaping.