C# I cannot understand why the code does not work

Ok this is the basic course of c# the final task.

We've updated our previous CheckSpeed method to return a string value. Update the method body with this logic:

If the speed parameter is over 65, return the string "too fast". If the speed parameter is under 45, return the string "too slow". Otherwise, return the string "speed OK".

I cannot understand why it wont accept my solution since it works fine on visual basic 2019 My solution is as follows

using System;

class Program {

static string CheckSpeed(double speed)
{
         if (speed > 65)
        {
             Console.WriteLine("too fast.");
        }
        else if (speed < 45)
        {
              Console.WriteLine("too slow.");
        }
        else
        {
             Console.WriteLine("speed ok.");
        }

        return Convert.ToString(speed);

}

static void Main(string[] args)
{
    // This should print "too slow".
    Console.WriteLine(CheckSpeed(44));
    // This should print "too fast".
    Console.WriteLine(CheckSpeed(88));
    // This should print "speed OK".
    Console.WriteLine(CheckSpeed(55));
}

}

The error I get from that code is Bummer: too fast. We called CheckSpeed(65.5), but we got a return value of: "65.5". We were expecting "too fast".