1992 Ford Mustang clutch cable

I just had a new clutch, throwout bearings, and pressure plate installed in my mustang, but after driving it less than 200 miles the car does not want to go into gear. When you put it in 1st. It starts to creep forward and is very hard to get into the other gears. Is it possible that the clutch was put in wrong? I also put a H- pipe on the car as well and someone told me maybe that the heat off the pipes and manifold are heating the cable and it is stretching, is this possible?