Sadie, you can do it! I just starting riding in late March and began training for the MS Bike 150. I did 79.8 on Saturday and rode back 79.6 miles on Sunday! I had those same feelings but you will be fine. Stay relaxed, so at your own pace, drink, drink and drink when you aren't even thirsty. It is better to stay ahead of hydration instead of being behind. Drink even before the ride begins. Also make sure you eat. Eat a really good meal with lean protein and some carbs the night before the ride. If the hill is too big, get off and walk and call it cross-training. You will be so proud of yourself. What is your longest ride?