I did this with my first sock. I think it had something to do with the way my needles were positioned when I made the join. Make sure that the needle that has your first cast on stitch is on the left. The last cast on stitch should be on the right needle with stitches on the middle needle in the back. It will look like this:
Make sure that when you join, you join the two needles in the front.
This has solved the problems for me.