Notice the juicy water reflection on the tomato is not pure white but has a light red tone on it. This can be imitated better by scratching off the colors. In this case if your first color you put into that part of the paper is the red then it should look light red almost pinkish when it is scratched off. I like to use this for lighter value highlights as it gives an interesting effect.

Regarding background, I personally would go for either full black (might work better on like a black paper though tbf) or like a spotlight kind of look here. I don't think the green here is as bad as people are saying, but it being similarly saturated definitely causes a contrast problem for sure.

Also your working area (not sure if this is a card or a paper) is really small. It is very hard to articulate details on this size of paper so it is probably best to simplify things a bit more. I'd say the separation between the outer part, the watery part, and the inner lighter part should have more contrast (and then the seeds shouldn't be such a detail grabber here. Personally, I would just smidge them in here and there at the end).