C++ Incorrect mouse movements

Question

I write a basic mouse movement code. I set cursor to move 50px left each time. But its move more than I set.

Code:

#include <iostream>
#include <Windows.h>

using namespace std;

int main() {
    POINT p;
    SetCursorPos(1920, 540);
    while (1) {
        mouse_event(MOUSEEVENTF_MOVE, -50, 0, 0, 0);
        GetCursorPos(&p);
        cout << p.x << endl;
        Sleep(2000);
    }
}

Output:

I tried to rewrite it from scratch.

Output should be:

1870
1820
1770
1720
etc...