Hi Gorgy_Love,
Like Cindy, I feminized my first name, and since I've always been informal, told everyone that my friends call me Steph. That simplifies things by keeping my initials the same. The middle name, though, I spent a lot of time thinking about until I came up with something very meaningful, and I'm surprised that it's even had an emotional effect on those I've told about it. So you could stick with the first name you've already picked, make the meaningful one your middle name, and start using it, just like Cindy has.
Or better yet, just change the first one now before people get used to it. All individual and family dynamics are different, and only you can judge how the people in your life will respond, but I've found that most people really appreciate openness and honesty. You could use your grandma to help you with this, by just stating that after having a heart to heart talk with her, and doing some thinking about it, you've reached the conclusion that you picked your new name in haste, and have found one that has more meaning and suits you better. If they care about you they'll be honored to be included in your thought process, and should have no problem adjusting, especially since this is all new to them anyway.
Good luck and don't stress about it. You'll be fine.
Steph
PS: I chose my middle name by starting with a pattern that would flow when saying it with my first and last names. Then I went looking for a musical term, since I've always loved music, to hear and to make. I found one that describes a musical style that's defined as improvisational, appropriate since I'm making this up as I go, and joyful, and I'm certainly happier now. My middle name is Rhapsody.