I would definitely recommend using Photoshop for this instead of Illustrator.
You might try playing around more with colors. Look up some reference real burn paper to see some reference colors. I see much darker black burn at the edge and lighter yellow orange around the inside.
Work with a separate layer for each color so you can adjust each independently.
I would set the brush hardness pretty low and with medium opacity so you can slowly paint in the burn gradually.
Hope this helps!
You might try playing around more with colors. Look up some reference real burn paper to see some reference colors. I see much darker black burn at the edge and lighter yellow orange around the inside.
Work with a separate layer for each color so you can adjust each independently.
I would set the brush hardness pretty low and with medium opacity so you can slowly paint in the burn gradually.
Hope this helps!