My first excursion with the StyeArc Barb pretty much encountered the same problem.  I made up the pattern, choosing the size that matched my measurements ... well actually if I went on measurements they should have been a bit tight.  Instead the resulting pants were HUGE .... not only wide at the hips/waist/thighs .... but too long, long in the crotch and too high at the waist.  It was like the entire pattern was increased by 20%.  I put the pattern away for the moment, as I just don't get where it went wrong. 

I have had some luck, with shortening tights on my regular sewing machine, rather than the overlocker.  I put some sew-in interfacing under and on top of the tights, stretch them slightly, and then sew across the leg with a tight zig zag or lightning stitch (stretch stitch).  I will go over the seam a couple of time to be sure, and then trim back the excess tights, and interfacing.  The seam is still a bit bulky, but not as much as the overlocker.