New Shower Cartridge leaks through handle

Hi Guys,
I have a question on a shower cartridge I'm replacing. I've tried this twice, both with a new cartridge, and had the same problem.
Here's what's happening.
My shower has a slow leak, so I took out the shower cartridge, took it down to the plumbing store, and got an exact replacement. It's an older type of cartridge, plastic, with two holes at he base, that match up with two of the three incoming holes in the metal fixture attatched to the pipes.
When I turn the water back on, the shower still leaks, and when you turn the shower on, water comes shooting through the cartridge where you would attatch the handle. Am I missing something? Whay is this happening?
Should I just try to do a whole new unit?
Thanks!
Ken

faucet

Whats the name on the faucet and or cartrige?

I will have to look on the receipt tonight...I will let you know. Thanks!