+1 on above.
Is this your first Mustang? The clutch on a stock Mustang is somewhat unusal. It has a quasi self adjusting clutch cable. Because of the way the adjustor works, the throw out bearing is in constant contact with the pressure plate. This gives the impression that the clutch is engaging too high.
As suggested, try activating the self adjuster. With your toe, pull UP on the clutch pedal. You will feel the quardant release. Push the pedal to the floor and back up a few times. Drive it. How does it feel now?