Every Thursday night, SCSwat hosts a Boot Camp that from what I hear is extremely helpful and informative. That's only two days away so you should get into it. I wish I could go but again I have stuff on Thursday.
Anyways, just keep trying. I switched from TF2 and I know first hand how long it takes to get used to. The first few rounds I had 0 points. Once you get a feel for the map, learn where all the good hiding spots, and follow Jedi or Capy around then you it starts feeling more familiar.
I will say, though, play both teams as much as possible. If you play as Insurgents and get see some really good hiding spots people are using, the next time you play Marines you'll be wary of those specific spots.
Anyways, welcome to INS and have fun!