You probably figured it out incorrectly. I'm not familiar with your arrow, but if it's the one that weight 9.9 gpi, then your FOC would be around 7.5%. If it's the one that weights 8.4 gpi, then FOC would go up to 8.5%. Either way, very low for a broadhead.

Your arrow is likely very stiff for that light tip. I'd try shooting it with a 125 grain tip and see if that doesn't help with arrow flight. Arrow length is also important, and if your's are shorter than 27", then it will react even stiffer.

Making changes will mean that you have to re-tune your bow. You may or may not have to move anything.