Eh... 64 qt..?
Adult BPs can live in 32qt tubs; 64 is likely to be WAY to big.
Temps and humidity will be hard to control in that tub... do you and your snake a favor and return the pad and tub. Go get a 15qt or something (if she's a younger one) and a 32qt if she's a little older. Then buy a pad that will cover about 1/3 of the floor in that tub.