If a girl doesn't want to add me on snapchat is that a bad thing?

I've been talking to her off and on for quite a bit. We don't run in the same circle of friends or have any mutual friends really.

She runs in your cliche highschool popular girls clique but she isn't as bad as you would think. I noticed that when her friends are around she seems to ignore but I get glances from her and when I catch her they shoot away very quickly. With other girls or people it doesn't happen this way and we ignore it. I've tried forcing eye contact across the room with other girls but it never happens because they simply never look this way but with her it's a different story.

When we are alone every time without fail she gives me this sweet bright smile and looks me in the eyes. It really surprised me the first time it happened. I smile back at her but never a word comes across us.

So I decided to be more bold. After class I tried talking to her asking about her day and how things are going. When I talk to her things seem to be going fine. She never once brushed me off or made excuses not to talk to me. Although for a pretty social girl she became more quiet.

One day I decided to add her on snapchat. I waited the whole weekend and I still didn't get anything and she's always on her phone. Next day at school I asked her if I could add her and she said she would add me back when she had connection. Since then she hasn't added me back.

I was pretty heartbroken over this because I took it as she didn't want to speak to me anymore. Is this the case? Is it because of the clique she runs in and because you can see mutual friends on snapchat she doesn't want other people finding out? Or is this just normal and I'm taking this too seriously? Should I just ignore this and keep trying?

I understand you shouldn't want to date a girl who doesn't care about you as much as her popularity but this is something that will change near the end of highschool when she realizes it doesn't really matter and your true friends will like you no matter who you date.