Do you think it's okay if I apologize to my ex?
Will they be open to an apology? What happened?
I need to say sorry to her face because i was a real asshole to her
If you feel regret about how you treated a past romantic partner, it's perfectly acceptable to want to make amends to that person. As long as you are genuinely sorry for what you have done.
I'm going to do it right now.
It sounds like you are making a mature and thoughtful decision by apologizing to your ex. Just be understanding if they don't accept right away, give them time to think and feel what they need to feel.