The pattern says: 16 sts and 21 rows is 4 inches with size 8 (US) needles using a double seed stitch.
My results are: 20 sts and 21 rows resulting in 4 inches with size 8 (US) needles.
If I understand right, this means I need a larger needle, but how much larger?
Its a crap shoot....LOL (that helps i know...but stay with me on this...)
When you do a gauge swatch and measure it, and its got too many stitches within the 4 inches, you need to take some away, right?
A larger needle will give you less stitches because it makes bigger stitches.
If you do a swatch and it doesnt have enough stitches, You need to add some...use a smaller needle because it will make smaller stitches and more stitches to your 4 inch gauge.
You need to take 4 stitches away from your 4 inch swatch. You need to use a larger needle. Now in your case I would step up to a size US 10 since you used a US8 for the first try and you are way off on getting the right amount of stitches in your 4 inches.
If you were just a little bit off...say 1 or 2 stitches, I would just stair step it up (go up one needle at a time), till you get the right gauge.
You know how you knit...so getting the right gauge means you need to make a guess, based on the way you knit, and which way you need to tweek your stitch count, on what needle you need to move to if you dont get gauge.
I dont even try to use the needle a pattern suggests anymore because I know Im a tight knitter and i wont get gauge with the suggested needle, I always start out doing a gauge swatch with 2 sizes larger. and tweek from there.
But not doing a gauge swatch isnt an option, if you want what your working on to fit like the pattern suggests. This is easy stuff once you can get your head wrapped around it.....
heres your mantra......to many stitches??? larger needle
not enough stitches??? smaller needle.
sorry for the long winded post ....sometimes i just go on and on and on...................................