Good luck!! It’ll be a great experience!
A few things you might not expect…
It won’t be a steady pace. There’s times you’ll be cruising, others totally in the red. Be aware of what’s going on around you. Don’t make any sudden moves in the bunch. Be aware of where your front wheel is at all times, but don’t have your eyes glued to it. There will be some shouting. Don’t worry about it. As soon as the race is finished it’ll be forgotten.
That’s a fair bit of climbing - rolling or some big climbs? If there’s longer climbs the race will spilt up. You’ll find yourself in a group of guys that can climb at a similar pace. If the road goes up, it’s going to come down. The descents will be fast. If I can’t pre-ride a course I’ve not raced before, I’ll go round it on Google Streetview to get an idea of road furniture, surface, technical sections etc.
A race of that length, I’d suspect it’ll take you around 3hrs. Plan your fuel/hydration accordingly. Race day isn’t a time to try anything new.
Have a look at the RaceSmart videos on the British Cycling website. The will give you a grounding in what to look out for and how to, well, race smart.
Above all, enjoy the experience. The rush from riding in a proper road race is like nothing else. You’ll love it😍