Garter stitch is knitting every row, which you didn't seem to do. It has bumps, but with a knit furrow in between them. The back of a knit is a purl and vice versa. When you alternate rows of knit and purl, that's stockinette on the knit side, and simply purl or reverse stockinette on the back - every row is a bump, not at all like garter. Stockinette curls which is why your knit a few stitches in garter on both edges to prevent it. After you're done, you can put on a border.
sue- knitting heretic