Re: lime, yes, it looked brighter and fresher on the polaroid, but I think I shifted something and it ended up like this. My teacher said the same thing. Didn't use a softbox on top, but I used a snoot(is this how you spell it?) for the strawberry.
your 'white' background could have been better i.e. cleaner and whiter if overexposed. overall, shot looks underexposed. with overexposed background, one will be able to see light streaming through the sliced lime.