It's a really straightforward route, no hills to worry about, small climb out to the 444 and Shenton Lane back into Bosworth. Fenn Lanes nice quick part of the route. If you're still building your confidence on main roads, you can come off the 444 not far after the Cock Inn and head via Upton village back to Fenn Lanes. (I'm sure if you google map the water park you'll be able to work out the actual route and see if there are any variations you want to make whilst training)
Weather was glorious last year! There is a bit of climbing as Charnwood possibly only area of the county with some cat 4 climbs ( I think Beacon Hill is classed as a 3, but as said before, it's not on the Autumn route)
second GraemeK's comment! Just keep working on those miles and maybe head over to Ulverscroft area on a longer weekend ride ( via Thornton and Bardon) and do some repeats round Polly Botts Lane area.
Good stuff Tri, glad it all seems to be coming together. See if you can get a few hill sessions in before October so there won't be too many surprises for ToNF - at least the Autumn route misses Beacon Hill but then you'll be ready to take that on when doing the 100k next May!