It's a great realization, and I am glad that you want to make amends. You also care for her feelings. Please make sure you tell her the truth. I know that you may feel guilty and shameful for leading her on. Don't step back, if u can apologise these feelings are easier to deal with. She may resist, may stop talking but that is a risk you must be willing to take if you want a closure to this.
If she comes back, you will be happy and vow to never lie to her again. If she does not return to you understand that in the Adult world failures and falls are part of love and move on. This will be a learning for the rest of your life.
Next Steps
seek counseling and support with someone you trust.
while speaking the truth to her, speak your intentions I am sure she will understand.
apologize to her without any expectations.
Health Tips
Don't get aggressive, remember you are dealing with hurt and painful emotions. So is she. At any point you feel you are not able to handle it, get back to her after sometime.