Serial data received more data than what was sent

Win32Port serial = new Win32Port("COM1", 38400, -1, 8, 2);

FILE * in;
in = fopen("data.txt", "r");
if(in == NULL)
{
    return -1;
}

int lineNo = 0;
char data[1025];
for(lineNo = 0; fgets(data, 1024, in) != NULL; lineNo++)
{
    printf("Line %d has been read.\n", lineNo);
    
    serial->write(data, strlen(data), 1000);
}
fclose(in);

HANDLE hCom;
hCom = CreateHandle("COM1", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_FLAG_NORMAL, 0);
if(hCom == INVALID_HANDLE_VALUE)
    return -1;

if(!SetCommMask(hCom, EV_CTS | EV_DSR | EV_TXEMPTY | EV_RXHAR))
    return -2;

DCB settings;
GetCommState(hCom, settings);
settings.BaudRate = 38400;
settings.ByteSize = 8;
settings.Parity = 0;
settings.StopBits = 2;

if(!SetCommState(hCom, settings))
    return -3;

COMMTIMEOUTS cto;
GetCommTimeouts(hCom, cto);
cto.ReadIntervalTimeout = 0;
cto.ReadTotalTimeoutMultiplier = 0;
cto.ReadTotalTimeoutConstant = 0;

if(!SetCommState(hCom, cto))
    return -4;

char buffer[2049];
DWORD size = 2048;
DWORD readSize;
COMSTAT comstatus;
FILE * out;

out = fopen("results.txt", w+b);

if(out == NULL)
    return -5;

ClearCommError(hCom, NULL, &comstatus);
size = min(2048, comstatus.cbInQue);

while(size > 0)
{
    if(ReadFile(hCom, buffer, size, &readSize, NULL)
    {
        fputs(buffer, out);
        fflush(out);
    }
    else
    {
         FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, 0, GetLastError(), 0, buffer, 2049, NULL);
         printf("%s\r\n", buffer);
    } 
}

fclose(out);