Fit test of 70 and need a colonoscopy. So worried as I only had breast cancer a year ago. Has anyone had anything similar?

Good morning everybody just had a call from the GP to say my fit test is 70 and need a colonoscopy I had Breast Cancer 12 months ago and now I am worried and crying today I am being treated for Gastritis with Esomeprazole which is making me constipated so I am hoping it is nothing has anyone had similar issues to me Thankyou