How do I fix uneven rows. this is my first crocheting project. just doing single stitch, but?

Yes, undo your work. And you have to gl in the lat stitch in the row. It usually doesn't look like a stitch, but there is. Even just going into the side, (end lf the row) once will do it. But say you started with 10 chains. You should have 10 stitches in every row from then on. So just check your work and keep making sure there is 10, and if there is not, check to see you got in each stitch, and that you went in the last one! Hope this helps! :/