Looking at it from the outside it’s incredibly easy to see that there is noting real here to worry about. It’s a woman well past the fertility prime who has had her tubes tied who had sex once with someone who pulled out. You pulled out of a woman who is for all intents and purposes sterile. Your worry is not based on reality at all, which is why I’m trying to explain to you that this is completely a production of your anxious mind. Since you’re already in contact with health care I think it would be a good idea to contact your therapist. The “problem” here isn’t the situation itself, it’s your unhealthy reaction to it. If you’re having trouble letting go of this event and relaxing, reach out for someone professional or a good friend that can help you calm down.
Posting about it here is pretty ill advised. People here are not health care professionals, and if they are they won’t try to treat you via an online forum. You’re more likely to get shit stirrers or people attacking you rather than actual help here. Get in touch with a real life person or just realize that there is nothing to worry about and do something relaxing.
I doubt that she is pregnant and the only advice I can offer is, “start wearing a condom.” I mean right now not at some time in the future when you think you’ll need one. If you had used this approach before meeting your inamorata you wouldn’t have this problem.