Listen carefully that tubing you got is 3/8" OUTER DIAMETER
you want tubing a snap larger than 3/8" INNER DIAMETER
OR LIKE THIS:
PVC Tubing with 3/8" inner diameter.. the pump is NOT wrong.. i have used that pump with 3/8" tubing
sorry for the caps.. but hey just get new tubing m8 its no big deal.. just ask for PVC tubing with a inner diameter of 3/8" .. hope im helping yah.