Is it normal to feel left out of your friend group because you don't fangirl

I think what you're experiencing is normal, but only because as humans we have a desire to fit in with our peer group. This is especially true of someone your age and even more so in the case of junior high school-aged individuals. I personally think that you are more the normal person than your so called friends.

I'm not trying to be mean or anything, but I do believe that you would serve yourself very well to look for some new and more interesting friends. Try to concentrate on your studies, hobbies, interests and the like. Your friends are behaving more like middle school students than high school students. I think you could stand to take a chance on finding new friends with whom you have more in common, and are thereby are more compatible with. You will be much happier in your life if you seek greener pastures than if you stay with these idolatrous, lame ass, hormonally driven, little girls.

Oftentimes girls like those you're describing exhibit what is very much the worst of what the female gender has to offer, not that there aren't males who do the same, but either way it's lame. There are better things to do than idolize and pine over complete strangers!

Your friends are being silly and young, and RoseIsabella is right on this one.

Look, I'm a BTS fangirl. As well as a lot of other groups...but I do have some things to say to help. A lot of people find it hard to differentiate faces, especially with such large groups in the kpop industry. If you don't want to learn about them, don't. Your friends should understand.
For me it's the reverse of your situation. I love them but my friends think I'm weird. The only difference is they know I'm love them (however its more than they think). But I see your point. I don't love just their music. You see, I love who they are as a person. I don't know their blood type and birthdays and all that by heart. Nor do I know the colour of their hair during different music videos and other stuff. That's not how I fangirl. I fangirl when I see J-hope cheering everyone up when their all exhausted. Or when one of them stays up all night just to get a single part of a dance right. Or when they cry on stage because of the emotions they feel. I love the relationship ungkook, Jimin, and V have and I wish I could have the same with my friends. I love how RM cares about every one of BTS and the fans. And I love how Suga shared his birthday with as many fans as he could. I love them all because they deserve it.
And if it turns out everything was a lie, then I'll fully admit that I loved them because of the side they wanted us all to see. But if there's no hardcore evidence then I stand by them, no matter the rumor, because they love each other and they love army (fans). And they prove it and I'm lucky to say I'm a fan.

I think that it's completely normal that you feel this way!

Let me just start off with me admitting this: I too love bts and exo along with various other groups, but I don't think you should try to force yourself into liking it!
I do admit, I myself are one of those girls who knows all of the members and the lyrics to every song, and YES, I know tons of stuff about them, but that's just me! You shouldn't be forced into liking everything your friends like either. Maybe you could try finding another hobby you enjoy, maybe your friends will like it too? If they're so incredibly stubborn, then you can always kindly confront them about you feeling left out.

You should push your friends off a bridge and watch their organs scatter on the rocks below.