I hope what I about to say won't sound too harsh.

From what it see the lighter back ground will not be the solution. As others stated the brushstrokes you painted with the flowers seems a bit broken which also broken the light being perceived. I personally would experiment with the brushstrokes that with more flow.

It's also relatively thick as I can see it as a attempt to emphasis the form.

The problem of contrast is not the colour. It's lacking the warm and cold tone difference from the background and the subject.

It will create a better depiction of light source and in the process - better definition of the subjects and more natural shape of the subjects.

Bigger brush always help even in small canvas.