After chemo where now?

My husband Tom (28) was diagnosed with Colon cancer in Jan this year. Thankfully the lymph nodes were clear despite initial fears as they were inflamed. Cancer was labelled 2B. It was a T4 tumour. The cells were moderate to poorly differentiated which are not the best kind. 6 months of Chemo is finishing soon. I am terrifed and unsure how to proceed. Tom's oncologist does not fill me with great confidence as we haven't seen him since January and there are some other worrying aspects of the care that bother me.
I would appreciate any advice. What should happen at the end of chemo? I only know about the colonoscopy and the CT scan. Is there any blood test that can be done regularly or other things we can do to stay alert to cell changes. He tested negatively for lynch syndrome.