Can HIV Be Contracted Through Protected Sexual Intercourse?

I had sex for the first time in my life with a sex worker 2 days ago. we have protected sex and after I ejaculated and my Penis shrink almost immediately which causes the condom slip and stuck at her vagina. When she realize it. It have some slippage of semen on her vagina but the condom did not broke. I have been reading your forums since morning, my concern is: 1. What are my chances of getting infected from HIV/STD 2. I have been feeling guilty since morning. Please tell me If I be 100% allright? Do I need to undergo any HIV/STD test. I didn t do any oral sex on her, except touching her vagina. Please Help! I am really freaked out.