I just had this same problem. Before you cancel, try unstalling everything from McAfee. Then reinstalling. Worked like a charm for me.
'Want to cancel.....could not install
Without any details whatsoever there's not much advice I can offer other than did you check that your system is compatible with the minimum System Requirements? Did you remove any previous protection software completely using removal tools as applicable before trying? Did you check for malware as that can prevent the software from installing too?
That said, this group can't get your refund for you. You have to speak to Customer Service for that. They are available through the McAfee Support link (top of page) > Home and Home Office Support > click "Go to Customer Service" in the middle of that page. McAfee offers a 30-day money-back guarantee.