After completing one round, still go up two rows to make the next stitch. Continue in this manner until you have reached the desired length. A double knit does not draw down to double length, but approximately 1.5 times the original length, more or less, depending upon the diameter of the finished chain desired.
For an even more dense knit, go up three rows for a triple knit. This knit will be very stiff if made with 24 gauge wire. It is usually made with 28 gauge or thinner wire.