I agree with rjc149, but I think there's something you can learn here.
I asked for it and she said no the first time. So I continued the conversation. And escalated it to some sexual stuff but nothing serious. Now, I tried to ask for her number again in a goofy way saying we can't talk about this stuff(conversation was about serial killers and pretty much around this topic) here and WhatsApp has better privacy so let's talk there. And she said no, we shouldn't talk about such stuff then which is basically no again so I completely bummed out and Said yep and closed the conversation which is not good right? Did I completely mess up? Do I still have a chance?
It’s very unlikely for women to give out their number after having a conversation with someone on IG under normal circumstances.
Most guys have a regular conversation with a woman, try to make her laugh and like him and then make an excuse to get her number. Don't be one of those guys.
When I've spoken to women online and want to move the discussion to WhatsApp or even on the phone, here's what I do.
TLDR
Steal her lines, and say out loud what she might be thinking, but direct it at her instead.
Don’t talk to a woman you’ve only spoken to online about sex or any of the sort, don’t even have serious conversations.
Rip on her. Think about it, you’re talking to someone online that you haven’t seen physically (other than their “supposed” photos on IG).
I tell them it's weird to talk to a random person on Instagram, and for all I know she can be a catfish, and how ironic it was that the conversation we was having is about serial killers.
“When were these photos REALLY taken?”
Make up a hilarious story of a time you spoke to a supposed woman on IG and when you spoke to them it turned out to be a 13-year-old boy.
And then qualify her by getting her to show “live selfies” of herself and eventually talking to her on the phone.
The point is your perceiving yourself as having high standards and not replicating the regular conversations she normally has (in a good way).
If she has a problem with this, then you can move on.