I was in a super similar situation! I got accepted into my top choice (yay!), but I still had one interview to go. I had some concerns about the program, and was really tempted to not go to the interview. My friend, whom I met on a different interview, was also scheduled to go to the interview, but decided to back out at the last second. I asked my undergrad mentor what I should do, and he convinced me to go on the interview anyway because at the very least, it's an opportunity to network and meet new people. I'm glad that I went, because it was a nice program and had really nice people, even though I ended up sticking with my top choice. I don't know what the program thinks of my friend, but I didn't want to risk it, especially since my area (forensic/correctional psych) is somewhat of a small world. You should definitely do what's best for you, though!