(My response is speaking by the pictures online. I can't really see the light arrangement, what type (size/shape/etc) hoods you have are and still didn't mention the exact # of plants there.)
Rather than get another light, I'd just reduce your plant count. You'll end up with more flowers with less plants getting the right amount of light, rather than more plants not getting enough light. Hell it's only the beginning of September, throw a few outside.
As far as fire risk if you add more light. One line running 2 ballasts (unless it's 100% dedicated), plus extension cords all over. That is sketchy already. I will run an extension to a T5, that's about it.