how do I fix my program that "slows down" windows clock time?

I asked a similar question recently, however none of the responses ended up working. The main difference now is that I have the logic for the program yet I still don't know why the clock runs faster than expected.
Anyway, I have a program that should slow down the speed of the windows clock by whatever percent I request. For some reason, it appears to make the clock run faster than I expected and I can't figure out why. The issue doesn't appear to be in the logic, as I've tested it with a large variety of numbers. I believe the issue lies in the optimization but I could be wrong

#include <iostream>
#include <windows.h>
#include <stdio.h>
#include <sysinfoapi.h>

int main() {
    int timeFactor;
    SYSTEMTIME lt;

    std::cout << "Enter a number 1-100: ";
    std::cin >> timeFactor;

    GetLocalTime(&lt);
    long timeBefore = lt.wMilliseconds;//975
    while (true) {
        Sleep(100);
        GetLocalTime(&lt);//025
        long SC = lt.wMilliseconds;
        long timeDifference = lt.wMilliseconds - timeBefore;//-950

        if (timeDifference < 0)
        {
            long timeToSet = ((timeFactor / 100.0f) * (((timeBefore -1000) * -1) + SC)) + timeBefore;//1000
            if (timeToSet >= 1000)
            {
                timeToSet -= 1000;
                lt.wMilliseconds = timeToSet;
            }else
            {
                lt.wMilliseconds = timeToSet;
                lt.wSecond -= 1;
            }
        }else
        {
            long timeToSet = ((timeFactor / 100.0f) * timeDifference) + timeBefore;
            lt.wMilliseconds = timeToSet;
        }
        SetLocalTime(&lt);

        printf("The time is: %02d:%02d:%02d.%02d\n", lt.wHour, lt.wMinute, lt.wSecond, lt.wMilliseconds);
        
        GetLocalTime(&lt);
        timeBefore = lt.wMilliseconds;
    }
}