I too often shut out my girlfriend from the real me, my emotions, my feelings, what I want and don't want, and distance myself from her. I want to learn to become more emotionally available to have a deeper, closer relationship with her.

This is like asking to explain the edge of the universe, or how long it would take to walk around the Western Hemisphere. Very tough project!

Your girlfriend has told you that you are lacking in these areas, I gather.
I would start with a 3 part approach: first I would ask her to spend 3 minutes once a day telling you what she needs to hear from you, and then you spend 10 minutes together having a heart felt talk. Make it a mini-exam, time it, have her write what she wants to say down earlier, and ask her to be patient while you struggle responding. The reason for the time limits is to keep it from escalating into a fight or just complaining. It also allows you to know when the end will be for that day, and keep it from being too painful.
Second, I would sign up for therapy or group therapy, even a peer-to-peer one that might be free (especially if you don't have insurance). You probably learned this emotional distancing at an early age, and can explore it with help.
Third, force yourself to say something personal and complimenting to her 3 times a day - just some short little sweet thing. The rewards will be huge. Sit down with paper and pen and write some down. Sneak up on her with a big hug and a smooch while you say a few of them. It may be awkward at first; she will appreciate you all the more for the supreme effort. What does this have to do with the 'real you?' Everything. You tell her what you like about her, and that tells her what you want. You reveal yourself by telling people nice things about them.

How long have you been with her? How old are you both? I ask because sharing on such a deep level takes trust, and experience between you. Time and practice is what make it work. It not always pretty either o patience is a requirement to gain understanding.

I have learned to be careful what you ask for.