How do I get more Instagram followers (I follow back. See for more details)?

[SilverUnicorn12]

I got an Instagram about 3 weeks ago and I don't even have 60 followers. All of my friends have at least 150, and it's kinda embarrassing. I mean, I'm not the most popular, but I have a lot of friends. I'm a freshman in high school (15), but I don't have a specific clique yet. I do have a group of friends (though I'm not sure all of them fully except me, they're pleasant people).

Anyway, how do I get more followers? I announce on my tumblr and on my pictures that I follow back, but that doesn't really work. Within the first 5 seconds of posting a picture, 3 random people will like it. I don't have an issue with that, but they just like it and don't follow.

Being the groveler that I am, my Instagram is gilly_karon and I do follow back.

Anyway, how do I get more followers? I'd prefer not to use one of those sketchy websites (even though that's what I did for Twitter) and I'm definitely not paying for more followers.

Thanks!