the 12 stitches it asks you to cast n is for one repeat of the pattern.
when you say you want to double the pattern, do you mean you wish to enlarge to pattern, or that you wish to do more than one repaet of it. (one reapeat is a horizontal patch next to a vertical patch with a vertical followed by a horizontal above it.)
If you where simply enlarging then yes you would do k4 p4 k4 12st garter. If you are adding a repeat, then you would k2, p2, k2, 6st garter, k2, p2, k2, 6st garter.
What are you using the pattern for?
BTW. the picture acompanying the pattern shows 2 1/2 repeats of the pattern (aproximately)
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