Cant stop worrying I have cancer or I'm going to die.

I dealt with that kind of OCD yes. I would have panic/anxiety attacks about it from time to time to. It lasted around 7 or 8 months for me and has been gone ever since (that was about 3 years ago). It was just fear, irrational fear. And the stress from it would cause my chest to hurt, headaches, things like that. I think meditating on these verses will help you:

For God has not given us a spirit of fear, but of power and of love and of a sound mind. 2 Timothy 1:7 NKLV

Be anxious for nothing, but in everything by prayer and supplication, with thanksgiving, let your requests be made known to God; and the peace of God, which surpasses all understanding, will guard your hearts and minds through Christ Jesus. Finally, brethren, whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy—meditate on these things. The things which you learned and received and heard and saw in me, these do, and the God of peace will be with you. Philippians 4:6-8

I remember Googling a certain disease one time that I thought I had. I remember sitting at the Google search box and sensing the Lord's presence at that moment saying "it's going to be OK, you're going to be OK." I am not saying it will be exactly like that for you but that I believe the Lord would probably be saying the same thing to you in your situation.

I also had some friends help me through it (they didn't all know I had so much OCD, but simply having those friends around helped). I don't know how successful I would have been without those supporting relationships I had at the time. One time I mentioned to my friend that I was feeling bad/anxious and my chest hurt. He said he wouldn't have that and he rubbed my back a bit and it actually helped a lot. Having that relationship that says "hey, I'm here for you" helped.

I am sorry that you struggle with this fear. However, I would advise that you get regular physicals and express your concerns to your family doctor about getting cancer. I don't fear getting cancer but when I'm afraid from feeling like I'm under a spiritual attack, I sing Jesus Loves Me to myself. Read 2 Timothy 1:7. It is one of my life's verses. Take care.