creating a rotatedRect in a threshold image

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Hello everybody

I am trying to draw an ellipse based on some points that I assign from a Threshold in an image. This is the image

I used fitEllipse function with parameter, all of the points of all of the pixels in a vector of points, with this I thought I was going to get an ellipse in the center of the image, however I got this one

I would like to get something like this (of course it should be an ellipse, but I'm not an expert in graphical design with paint) in a way of ellipse or if it was possible to get a RotatedRect square like this, then it would be awesome too.

I also tried with contours, however the result is not also that good.

I would like your help guys. this is the code I am using

#include <opencv2/opencv.hpp>
using namespace cv;
using namespace std;
double thresholdValue = 0;

int main(int argc, char** argv) {

Mat src = imread( "/home/diego/Humanoids/imageGreen0.png", 1 );
Mat imageGreen = Mat::zeros(src.size(), CV_8UC1), threshold_output;
Vec3b result;

for (int i = 0; i < src.rows ; i++)
{
    for (int j = 0; j < src.cols ; j++)
    {
        result = src.at<cv::Vec3b>(i,j);
        int value = result[1];
        imageGreen.at<uchar>(i, j) = value;
    }
}

threshold( imageGreen, threshold_output, thresholdValue, 255, THRESH_BINARY_INV );
vector<Point2f> pointsPixels;
for(int i = 0; i < src.rows; i++)
    for(int j = 0; j < src.cols; j++)
    {
        if((int)threshold_output.at<unsigned char>(i, j) == 255)
        {
            pointsPixels.push_back(Point(j,i));
        }
    }

RotatedRect elipseBottle = fitEllipse(pointsPixels);
ellipse(threshold_output, elipseBottle, Scalar(125), 2, 8 );
imshow("threshold ouput", threshold_output);

 return 0;
}

I would be very thankful to you if you guys could help me with a solution or at least ideas (by now I will keep checking at rotatedRect functions or fitEllipse in case I did something wrong). Thanks a lot.