is it falling down from weight or from the cable being too tight???
ditch the adjustable cable and put the oem cable back on with a firewall adjuster.
What you are describing is almost impossible if you have it setup right. Be sure the cable is hooked onto the quadrant, and hooked onto the clutch fork under the car. If it's hooked at both ends, the quadrant is properly pinned onto both pins, the clutch pedals will NOT fall to the floor.
does it stick to the floor, and if you pull it up it snaps back down?? If so, somethings binding and pulling it back down.
you could have misrouted your clutch cable. Be sure it goes straight out, past the shock tower, then routes down and UNDER the car right where the steering rack and oil filiter is.