Ok. So you did a lot of mistakes here. Let's clear it out :)
First. Why you mixing 1:1 red and cherry and then add extra BLACK pigment? Are you sure what are you doing and why?
Do you intend to cast them? Then no black! It's carbon and it's very bad for castings. If you want to achieve better quality then use original cherry. It already contains more pigment so you will not have to add any more. And of course slice thinner - second)
Second. Why you are slicing with such a pigmented mix (yes even 1:1 is quite highly pigmented, not to say you added some pigment) at the WHOLE 50z? It's to high! This exact resin mix will have hard time to curing such deep. So try to slice at 20-30z, or use pure original red with 50-70z slice height. Okay, maybe you could add splash of cherry to red to slice effectively at 50z. But splash (maybe 1:7 - 1:12), not 1:1, and don't add any black pigment.
Third. Never try to print model with such a big flat surface PARALLEL to the build table! Or you will have what you have now. Simple solution is to angle it slightly. Maybe 10 or 20 degree will help. Yes it will add some "staircase", but at least it could be successfully printed. Or try to print it vertically, still with, a lot of supports underneath.
Fourth. I'd add way more supports for such a big and flat part. If you current supports are ok with small models like you printed before, this exact needs way more.
Fifth. Superawesome skulls design! :)
That's all. :)