crystalle, what you can do is tighten up the first stitch which pulls on the last stitch just beneath it. And knit the first couple stitches in a row tight so there's less extra yarn accumulating at the end of the row. There are a lot of threads on loose end stitches, you can do a search for them.
Mods, can we have a sticky on the last stitch being too loose? That seems to be a very common problem and question for new knitters.