I feel like I've been talking about this for years, but I think I've finally settled on pharaoh's horses for my chest piece. To accommodate boobs, I might need to spread them out a little and maybe add flags/roses/stars/etc to make the overall design more triangular. I'm in no financial or mental condition to be undergoing a multiple session tattoo any time soon, but it might be my next big project. Thinking of getting this dude to do it: https://www.instagram.com/johnrippeyv/
I think it comes down to these as your options:
1) Laser it completely - Takes a lot of sessions to completely remove, which can get expensive and painful. Might not be TOO bad for something that size though.
2) A couple laser sessions to lighten it and then a cover-up - Gives you more options to work with after you break up some of that black.
3) Cover it as is - Unless you want a bowling ball or a tiny panther, it's going to need to be fairly large to cover it and not look like a cover, at least palm sized...and you would probably need a lot of dark colors to cover all that heavy black. You can have an artist look at it and see what they think might work, but be prepared for it to be much larger than you might want.
4) Add some vines and frilly stuff like @Dan said - It's only going to make the tattoo bigger and might still not give you the look you want if it's the backbone of the tattoo that you seem unhappy with...adding to it might just give you more to dislike. It's up to you though to decide if you want a complete overhaul or just some minor changes. Be honest with yourself about what parts of it, if any, you really like and want to enhance.
5) Get awesome tattoos elsewhere on your body and/or learn to love what you have - Sometimes trying to fix stuff just makes it worse and the best option is to just live with it and laugh it off as a dumb mistake. Surrounding it with awesome work takes the focus off it. Maybe not an option for you if you don't want to be a more heavily tattooed person. In that case, just try to accept what you have if lasering or a cover-up is really not an option for you.
Whatever you do, I would not suggest adding white anywhere. It tends to get yellow/brown with age and I think it would just muddy up the tattoo more. It isn't going to stay nice and crisp like Instagram always shows it looking.