Hi, I put your route in to myrouteapp.com and it comes out at 957 miles on the Tom Tom and Google Maps and 1024 on the Here (Garmin) map so you need to add some miles, perhaps head a bit further north?
You can send a proposed route to
[email protected] ahead of a ride and Martin (not me) will have a look at it for you. Here is a different route, unverified, for your consideration although you may have to take it slightly further north.
Good luck!