Jessica,
A few words of advice:
1. Do not drink too much, have one or two max depending on what your tolerance for alcohol is. If your "date" insists on trying to get you to drink more kindly tell him to f*ck off.
2. Do not be overly nervous. Nervousness telegraphs to others that something is wrong & will cause them to examine you more closely.
3. Someone recently posted on another thread that "people see what they expect to see". If you look & act female, that's what they will see.
4. Let your date order for you so you don't have to worry about your male voice.
5. Act confidently, walk in like you have done this dozens of times before.
Above all enjoy what is liable to be a very interesting & unique experience.