I don't know whether you can or not, but why don't you take the paint back to SW and ask them to retint it?

Sadly, we all learn the hard way that you have to do test samples before proceeding.

Buy black and be done with it....6 times is enough already. It probably is because they didn't mix the color with the right base to start out with.

Selecting a different color is the best solution. Adding tints to a partially used paint to try to arrive at some other color is a bad idea.

Welcome to the arena of REDS. They can be a real problem, although 6 coats seems quite excessive. I hope the people that tinted it for you at least warned you a little?
Reds do not hide. They are subject to the color over which they are being placed, as well as other issues.
Try picking/finding one that is ready-mixed and hopefully tinted with better pigments, not the colorants your paint store used.
You could also try another brand/quality of paint. You may be starting the project with a deep or neutral base that will not stand up to reds.
And finally, it has to be tinted correctly. Take it back to the store and check it out.
Good luck!