It is OK to have those thoughts and actually if you did not have them at some point I am sure it would be a strange thing.. Firstly you have your treatment doing its best to knock you around, well meaning friends who sometimes do not understand the impact of what they are saying can mean to you and of course then there are your children. All these things together with your diagnosis are a perfect storm to be thinking this stuff.
Everybody is different and we are all real people and any statistics you may come by are just a 2D black and white number. Remember that you are here right now and the chances are better than ever before that your cancer will not return. and I promise you that as you move further down the track and past your treatment and into your maintenance visits all those scary thoughts will begin to move further and further to the back of the list. But if and when they surface, it is ok to let them visit but dispatch them as soon as you can .
It may be helpful to try some meditation or relaxation (speak with the onc team about where you can find something) and if you cannot dispatch the feelings of dread then think about speaking with someone so they can help. But remember, these thoughts are normal during the journey
Sending you warm and calming hugs xxxxx