If you have an absolute nightmare, and are hating it, the route goes past Christ’s Hospital train station. https://www.southernrailway.com/travel-information/plan-your-journey/station-information/stations/christs-hospital

BUT…

You’ll be fine, keep going and you’ll get there…

I did it a couple of years ago and blew up at Cranleigh.
Unfinished business for me.
Eat and drink plenty, I now use Torq energy powder in my water and it has really helped with cramp.
But don’t go mad with products, just pack some jam sandwiches, fig rolls etc.
Stop at every food point even if you don’t think you need to.
Get a few longer rides in, 50 miles say over the next couple of months.
Don’t get too hung up on ‘what bike, what tyres’ etc, just ride what you have.
Enjoy it and remember a positive attitude gets us through most things.
Very important to get decent chamois bib shorts or whatever and chamois cream.