Hello

Can you please help me; I am relatively new to video editing (started with Windows Movie Maker and now progressed to Premier Pro)

I am trying to do the classic scene where the same person is seen having a conversation with themselves. I have filmed the person in the two roles (without moving the camera) and imported the video into Premier Pro.
I have placed the two parts of the video on two video tracks; I have then applied an image matte mask on the second track. The mask is just a Photoshop image left half black, right half clear.

This almost works. The problem is that the second person (video tract two) is very slightly transparent and you can see the background (video track 1) through the person.

Has anyone got any ideas?
Thanks in advance

PS
Machine spec is Dell 3Gig, Pentium 4, half Gig ram, not sure about the video card.