I am learning Python and trying to understand writing to a CSV. I need it to be in a header / row set up and keep getting a float error

import csv

FILENAME = "trip.csv"

def save_data(miles, gallons, mpg):
    header = ["Distance", "Gallons", "MPG"]
    data = [miles, gallons, mpg]
    with open(FILENAME, 'w', newline="") as file:
        writer = csv.writer(file)
        writer.writerow(header)
    with open(FILENAME, 'a', newline="") as file:
        writer = csv.writer(file)
        writer.writerows(data)

def display_title():
    print("The Miles Per Gallon program.n")


def calculate_totals(miles, gallons, cost):
    mpg = miles / gallons
    cost_per_mile = miles / cost
    total_fuel_cost = gallons * cost
    display_data(mpg, cost_per_mile, total_fuel_cost, gallons, miles)

def display_data(mpg, cost_per_mile, total_fuel_cost, gallons, miles):
    print()
    print(f"MPG on this trip is {mpg} gallons.")
    print(f"Cost per mile was ", cost_per_mile)
    print(f"Total fuel spent was ", total_fuel_cost)
    print()
    save_data(miles, gallons, mpg)

def main():
    display_title()
    
    choice = "y"
    while choice.lower() == "y":
        miles = float(input("Enter miles driven: "))
        gallons = float(input("Enter gallons used: "))
        cost = float(input("Enter cost per gallon: "))
        calculate_totals(miles, gallons, cost)
        choice = input("Do you wish to enter a new entry: y/n ")

if __name__ == "__main__":
    main()

I was trying to get an output into a CSV that had Distance, Gallons and MPG as a header with the rows underneath keeping user input data. I finally figured out how to make the header but now I am getting a float error and nothing I try seems to get rid of it. Any help would be appreciated.