I don't know bro. I tried the gentlemen route when I was young and it never went perfect. There was always something that could have been better.
I agree with the above advice that this girl will not be the one true love of your life and when you are 30, you are going to look back on this concert as a time when "X" went right and about a dozen things went wrong. LOL
You said you have been talking. Have you been putting on a front or have you just been yourself?
If you have been putting on a front, you are NEVER going to be as cool in real life as you pretend on line or on the phone.
If you have been yourself, then don't change! If you don't like a song, or a drink, or garlic fries, then say so. Don't pretend to be someone you aren't.
Don't sell out who you really are, because while this girl seems like the most important thing right now, NONE of us here are with the girl we thought was perfect at 14 or even 18.
If she wants to go to this concert with you, there is a chance she wants to go t be with you. There is also a chance she wants bragging rights at going to the concert to her friends. Never underestimate how petty high school kids of both genders can be.
I guess the best advice I can offer is don't assign any hopes or "what ifs" to the concert and go with the intent to see artists that you like, for reasons you want.
Then if anything positive happens, it's a bonus. If nothing positive happens, you still got to see a really great concert. Right?
Good luck and just be cool.