Ah, the famous end stitch. All your other stitches are attached at two sides and the end stitch isn't, so it's looser than the rest.
When you work the first couple of stitches, hold your yarn a little tighter--that can help.
The end stitches tend to naturally tighten up as you work the next rows.
Another technique is to slip the first stitch of the row. This means it only gets knit every other row, so it is tighter.
There are probably a billion posts about the end stitch, and I think it's the most common question for new knitters.