Question About lens size

I have a question concerning the size of lens and its focal length in regard to projecting a 5" lcd screen. If I have a 3.5" in diameter plano-convex lens with a focal length of 12 inches, will I be able to capture all of the 5" screen and project it? The reason I'm asking, I'm experimenting with a simple 150w spotlight, fresnels, and this plano-convex lens and I'm using a transparency picture (I printed it on a transparency sheet with my inkjet printer, a good cheap subsitute for experimenting with instead of an lcd) of approximately the same size as an 5 inch lcd screen. However, it seems to only project a "circle" of the center of the picture and not the whole thing. I'm thinking this is just because of the low-wattage, round spot light bulb and will be cleared up when I go with a larger light and proper reflector, but I would like to know if I need to find a larger in diameter lens or a different focal length to "capture" the whole image?