To create a negative space painting you have to work layer by layer allowing each to dry before continuing on. Because of this it can be a long process, so do not get descoraged if it’s not coming together as quickly as you would like it too. Keep going it will be worth it!
Don’t forget to check your values. To do this put both your painting and your referance picture in black and white. This will allow you to see if you’re on the right track. Check out my blog and video on values if you need more guidance on that technique. https://www.youtube.com/watch?v=FgQDtv0zJQA&t=9s
Check out the full video here to see the process and follow along!