1989 Ford Ranger Replacing fuel pump & sending unit.

Hi, I've been told that my fuel pump was bad so I went to replace it. I bought a pump and sending unit combo and dropped the tank and put it in. My problem is of the two lines that supply the fuel, the high pressure (I assume) pushes itself off and leaks. It has a fitting that locks around the nipple and I have pushed it as far as it would go ; as well as locked it multiple times. What could be wrong /I be doing wrong?? Second, would it be a bad idea to cut the fitting off and use a few tighteners to fasten the hose to the nipple?

-Thanks