Can't stop blaming myself - help?

This was our texting conversation yesterday, between my now ex-crush and I:

Me: I'm gonna (gun emoji - kill) you if you don't wish me a happy birthday today because we've known each other for almost two whole years. Lmfao jk!

Her: What? Eliza, that's really weird joking. I don't like that at all. Best wishes to you, but please don't joke like that with me.

Me: Oh, my apologies. I didn't think much of it - people tell me they are going to "kill" me if I don't/do do things to me all the time, but ok, I know now. I'd call you about this, but I figure it would be bad if you were in class today and you heard your phone ring.

Me (some hours later when I had a chance to text again): But you're right & I see where you are coming from now - death is not a joke.

She read my last two messages, but didn't reply. She seems upset to me. I wanted to call her because I thought that would be a better way to apologize to her since our college is huge and I almost never see her in person (like once/twice a semester).

Other Info: She's a friend (but not a best friend) I've known for 2 years, she does NOT know I like her romantically yet (I don't know if she's LGBT or not yet - I was hoping I can sit her down some day and talk to her about being into girls and stuff someday & her Facebook just says "female" but she's LGBT friendly from her social media posts), I told my friends about what happened and we are all shocked at how she replied to me.

I mean, I know what I did was wrong now and that there's no hope in getting in bed with her, from the way she replied to me, but I just can't stop thinking about this and blaming myself for it.

What would you do here? Help? Tweet