Of course you are paranoid - who wouldn't be? You're allowed.

I have been through cancer 3 times with my mother who was very forthcoming with her fears and had to wait 3 months for a kidney removal for renal cancer. She described exactly what you are saying. Unfortunately no matter how much you rationalise, there is that little voice in the back of your head that is telling you the cancer is spreading. Not so.

Try some positive talk - everytime you catch yourself thinking about the pain or cancer, firmly tell yourself that treatment is being taken care of in XX days, time to think about xxx. I try and work out in my head how long it would take me to travel to a place at a certain speed when I am "churning" about something (but I am peculiar ). I am sure you can think of something more interesting, but you need to work out what you are going to distract yourself with ahead of time and then make it complicated enough that other thoughts can't drift back. If they do, tell yourself again until that evil little voice goes away.

Sounds a bit airy fairy but it works for me and it worked for my mother - she re-decorated her lounge room in her head and then progressed to drawing her ideas on bits of paper and after surgery, moved house so she could REALLY decorate!!