If I read it correctly, you created a route A to B on your computer using BaseCamp. This was a three hour route, which had a pre-set start point (A) and a pre-set end point B in Burford. A and B are, by default, fixed. Between A and B there was a series of unannounced via points, used to shape your route when you created it. You stored this route on your GPS device.
I suspect:
1. That when you summoned up your route on your device, you might have been sitting some way off it
2. You were asked to chose your destination from one of the only two available choices: A (your pre-set start point) or B (your pre-set end point at Burford)
2. That you chose (B) Burford as your destination.
Your device then did as it was instructed to do, taking you from wherever it was you were when you started, straight to Burford, along a route it created based on your preference settings.
It's a common enough error. There are ways to help to avoid it. The simplest way is to look at the route you made, its shape, distance and total estimated time to ride. Then look at the route the device offers up when - in your example - you chose B. If it looks very different to what you expected then there's probably a very good reason why.
If does look very different, then you can fix the problem in several ways. Maybe the simplest is to do the equivalent of the old verbal instruction to: "Please drive to highlighted route". To do this:
1. Fire up your GPS
2. Summon up the A to B route onto the screen but do not run it
3. You'll be able to see your position cursor and the magenta route
4. Navigate yourself onto the magenta route, using the screen as a map, just as you would using a paper map / common sense
5. When you are sitting on the route, then start running it
All should then be well