It's very easy(says she who lives only 50 miles away)I think
Try this map http://www.multimap.com/map/browse.cgi?lat=53.5203&lon=-1.0965&scale=25000&icon=x if you zoom out you will see the roads & A1 relative to the race course
I had that happen to me once, a lady was following me to a dog show..... Only hers was a completely different show to the one I was going to!
We were both lost only found that out when I stopped in a layby to try and discover where I was going wrong (don't you just love schedule maps sometimes) LOL, but I eventually found the venue of the show I was going to but I never knew if she did find her show :)
A warning though a friend that travelled to Driffield show yesterday (Thursday) from the south said it took 3/4 hour trying to get to the racecourse from the motorway said traffic was bumper to bumper.....
Traffic at that time of the morning in Doncaster, especially from the A1, is always slow which is why I'm glad we're going on Sunday & coming from the oppostite direction ;)