Making hotel reservations with a significant other...when is too soon?

I tried to make this as concise as possible. My apologies for the length.

I have been seeing this girl since January (we had a brief break for about three weeks but we were still sleeping together). We're both in our early twenties and she is a couple of years younger than me.

I bought tickets for a concert several months ago and the original concert date was set for mid-June. I told her to save the date a few weeks before the show but I did not mention what we were doing. Shortly after she requested off from work the concert was rescheduled for October. Obviously, we didn't go to the concert and I never got around to telling her what we were doing.

Flash forward to the other night. Another artist (AFI) who she and her friend like is performing the same night as the rescheduled concert. She kept pestering me about why she should miss out on AFI and wanted to know what I had planned. I reluctantly tell her who I bought tickets to see and she is absolutely ecstatic. In fact, she becomes so ecstatic about the concert that she decided to take it upon herself to book a hostel in New Orleans for that night.

Here's my issue...I bought the tickets because I desperately wanted to see this artist perform, and not because I thought it would be a great date with her. I just figured that I might as well ask her to accompany me because we're currently dating. That being said, I didn't take it as a sure thing. You never know what can happen with someone in a few months, right? I have no problem with finding someone else to go with me. However, I think she is under the impression that I bought the tickets specifically for the two of us.

I didn't want to tell her about the concert until a few weeks before the show because if things were to go south between us I didn't want to upset her, aside from breaking up, by having her miss out on the concert.

My question to the OT is this: Is making a reservation such as this with someone you have been seeing for approximately six months a bit presumptuous (particulary something three months away)?