I had a similar issue about 20 years ago when I had a lump on my forehead and doctors couldn't tell me it wasn't dangerous because they didn't know what it was, even after several tests. I was very worried about it, and my imagination got me expecting the worst.
I would say that your anxiety is completely understandable and justifiable. It's horrible when you think something's not normal, and our negativity bias makes us think the worst. So don't beat yourself up about feeling anxious because it's a normal reaction, part of being human.
You can even think of your anxiety as having had a useful purpose, to get you to take action, which you have done: you've got an appointment with an expert. You've done really well to do that, so can feel proud of that.
But of course it doesn't stop there, and you can't help thinking about what's going to happen next, predicting the future, which no-one can do. We can't control the future because it hasn't happened yet, and when we feel out of control we feel stressed and anxious.
How about this: tell yourself that the best you can do now is get ready for your appointment, get there on time, and then you can leave it to the expert, someone who is fully trained, who has a wealth of knowledge and experience, and who will take good care of you. If you find yourself worrying about what will happen after that, just repeat to yourself: "I'll handle it."
It really is natural and normal to have some anxiety, but just focus on what you can control now (getting ready for your appointment, planning journeys etc), and assure yourself that whatever happens in the future, you'll handle it. Also, by practicing some relaxation and breathing exercises, which elicit the relaxation response, you'll be countering the stress response and reducing the stress chemicals and hormones (like adrenaline), which can only be good for you.
The law of averages is on your side too. The human body is amazingly resilient, and advances in medicine and technology make all kinds of treatments and cures possible. Just trust that it will all work out for the best and you'll be ok.
Wishing you all the best, take care.