As Fraser suggests above, it's an absolutely smashing day out and I'm sure that if you have entered and paid you are definitely in - from memory I didn't enter last year until late in the summer. I'd be going again this year if it wasn't for OWMTBC11.
The best bit in many ways is that you can decide mid ride which course to take (I'm thinking of doing the medium instead of long course rather than setting off for a 28km pootle and deciding it's good so going for 200km+) so if mechanicals or weather strike there's a ready made alternative option. Plus as it's a fairly circular route you can alawys cut back along tarmac roads if need be. I found having that safety net comforting, even though I didn't need to use it.
One last thing for now is to not underestimate the amount of climbing involved as Tuscany is pretty undulating with precious little flat - I chickened out to an extent and used a compact chainset but at least that meant I rode all of the climbs wheras there were several people pushing. Was the climbing in the long route close to 5,000m in total? Regardless, the fact that I rode it all may have had something to the generous glass of chianti that I had at 8.45 a.m. And 11.20 a.m. And 2 p.m. And 3.59 p.m. etc. You get the idea.
I suggest practicing cycling with toeclips and straps if you have been using clipless as it was more than 20 years since I had and although there was memory, flipping up a pedal and inserting your foot in one, deft motion does take a bit of remembering.
I'm sure I could waffle on for a while, indeed have done, but will stop for now.
Crucially, what bike are you taking?