I am 21 years Old. I feel VERY MUCH ashamed to reveal this matter with you, but no other option. Please help me. I have a sister who is 19 years old. One day we both were left at relative’s house and accidently we had oral sex (no intercourse) in the bed. We both were naked and I ejaculated in her underwear. This happened 2 weeks ago. I am afraid of my sister getting pregnant because of me since she was wearing the same underwear. I am very much depressed because of the sin done by both of us, but I guess she doesn’t care about this matter. PLEASE HELP

No she won’t get pregnant for sure.
You are already feeling guilty about what you did with your sister so I do not want to add to your guilt but can not restrain myself advising you to spare and respect some relations.