Hi there, and you've taken the most important first step, which is an acceptance within yourself and the ability to have come out to your girlfriend.
The hardest step is that initial one, you'll have to explore your own feelings in your own time, it may be worth while starting off small with a little bit of make up, dressing up underneath your normal clothes and going out like that and see how you feel in the big wide world, that's how I started and I found it was what was right for me, maybe have your girlfriend dress you up a few times in private and see how it feels, it seems she's very open and accepting of you already from what you've said. Take advantage of this and see if she'd be willing to, if you feel more comfortable and happy dressed, then well you'll have your answer to any doubts you're feeling one way or the other

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There are loads of people here who will help support you through any decision you make, I've spoken to a few already and they are all very nice and helpful

I am always about if you just want to talk to someone who has only just come out to friends and family, I know how anxious it can make you, but as long as you tell the right people, people who you feel will support you, you'll do well

HUGS AND KISSES xx