The needle size on the yarn label is actually more for putting a yarn into a weight class (fingering, worsted, bulky), rather than a 'recommended' size. Patterns will use a smaller or larger needle for a design effect - a smaller one gives a tighter denser knit, something you want with socks, while a larger one will give a looser, more open knit, such as for scarves or shawls. But in general the gauge and needle size is relative to the thickness of the yarn.
It's very easy with garter stitch to pick up new stitches at the beginning of rows. If the yarn is over the top of the needle to the back it can pull up the first stitch and each leg of it looks like a separate stitch. When you start, hold the yarn off to the side a little so you can see the first stitch easier.
sue- knitting heretic