Hi elsenior,
1. When using a tk2dCamera, ignore the settings on the "normal" camera. First thing to do: click on the tk2dCamera, tick Force Editor Resolution, and set it to 960 x 640. In the game view set resolution to 960x640 or 3:2. Now whatever you see in the game view is what you'll get in game.
2. If your level background sprite is too small, it probably means the collection wasn't created with "Use tk2dCamera" ticked. Try again with that ticked.
Always refer to the tk2dCamera preview window, rather than the other views. This is because of a bug in Unity (which has been reported, of course).
p.s. I assume that you're using 1.76 + patch1 on Unity 3.5.5