Late seroconversion is an old myth which you can verify on the HIV forum by either posting the question or searching other threads since it is an often posted question.
if you are afraid of a lancet you will never be able to get any blood tests done, so your comments revolving around why you can't accept what others do accept identifies the problem. Again that issue is a weekly new thread on the HIV forum so you can see responses or ask on your own thread.
I believe your post a few weeks ago said you were a nurse, so it seems therapy would be a potential aid in dealing with these 2 phobias, HIV and nurses infecting you. I listed it as 2 because it seems to be more than one problem.
Perhaps writing all the issues down beforehand to take to the 4/28 so you don't forget anything will help the 4/28 appointment get to the heart of the issue quicker, which will obviously provide quicker relief. Sometimes the first session of therapy is so emotional that the patient is overwhelmed and uses up all their time trying to settle down, ergo the usefulness of notes.
Fear of HIV is very real, and you are not alone. Many men and women are paralyzed with fear about the possibility of contracting HIV. My suspicion is that your anxiety extends to other areas of your life, not just a fear of HIV infection. A good therapist will help you work through your anxiety, which will take time to unpack and resolve.
Stay strong. I had a scare where a phone call from my doctor was misinterpreted as a false positive and I have tremors when I think about it. It helps to keep your mind occupied reading books, working on a project or spending time on hobbies. I wish you the best, my thoughts are with you. Anxiety can destroy you, fight back when you can. Give yourself the time to feel but realize the evidence you have in front of you. I also have an appointment coming up, I can't wait to get help overcoming my own fears.
You only have one problem, and it isn't HIV. It's the fact you're worrying yourself to death about it. Follow the advice above to seek therapy. You can't make life risk free, but you can hopefully learn not to ruin your life worrying about it.