Without seeing your keying settings, we can't tell you much. Provide screenshots. One thing's for sure: The lighting is completely whacky and the screen color wrong for a good green screen.
I'm using Keylight 1.2 to key out some greenscreen...most of the outlines always turn out really grainy... I'm using MXF files, and they are a tad low-contrast. I brought up the contrast, but that didn't seem to help.
What might I be doing wrong?
Why do people insist on using Crummy-looking footage in AE? Do they think "we'll fix it in post" bodes well for success? Do they think AE works miracles or something?
They're not a "tad" low-contrast, they're awful! Re-shoot if you can. You haven't given yourself any kind of fighting chance at a good, clean key. I'd google the terms, "lighting for green screen", "lighting for chroma key", etc. You'll learn a lot.
If you can't re-shoot, use your workaround -- key the footage as best as you can, and use it as a track matte.
The footage is a mess. It's going to be very difficult to pull a professional looking key from that footage. I would color grade as much as possible to try and separate the colors, pre-compose, then pull a key on the pre-comp, then use that for a track matte for the original footage if you end up having to foul up colors to get a decent key.