Why is my sobel filter code only returning half of the image?

Question

Im trying to do edge detection on my image without the already existing functions in opencv. I copied this code from somewhere on GitHub, but for some reason it only does half the image, I thints because of the image type but im not sure.

enter image description here

Mat Picture::sobelFilter()
{
    //Sobel X Filter
    double x1[] = { -1.0, 0, 1.0 };
    double x2[] = { -2.0, 0, 2.0 };
    double x3[] = { -1.0, 0, 1.0 };

    vector<vector<double>> xFilter(3);

    xFilter[0].assign(x1, x1 + 3);
    xFilter[1].assign(x2, x2 + 3);
    xFilter[2].assign(x3, x3 + 3);

    //Sobel Y Filter
    double y1[] = { 1.0, 2.0, 1.0 };
    double y2[] = { 0, 0, 0 };
    double y3[] = { -1.0, -2.0, -1.0 };

    vector<vector<double>> yFilter(3);
    yFilter[0].assign(y1, y1 + 3);
    yFilter[1].assign(y2, y2 + 3);
    yFilter[2].assign(y3, y3  + 3);

    //Limit Size
    int size = (int)xFilter.size() / 2;

    Mat filteredImg = Mat(_image.rows - 2 * size, _image.cols - 2 * size, CV_16UC1);

    angleMap = Mat((_image.rows - 2) * size, (_image.cols - 2) * size, CV_32FC1); //AngleMap

    for (int i = size;i < _image.rows - size; i++)
    {
        for (int j = size; j < _image.cols - size; j++)
        {
            double sumx = 0;
            double sumy = 0;

            for (int x = 0; x < xFilter.size(); x++)
                for (int y = 0; y < yFilter.size(); y++)
                {
                    sumx += xFilter[x][y] * (double)(_image.at<uchar>(i + x - size, j + y - size)); //Sobel_X Filter Value
                    sumy += yFilter[x][y] * (double)(_image.at<uchar>(i + x - size, j + y - size)); //Sobel_Y Filter Value
                }
            double sumxsq = sumx * sumx;
            double sumysq = sumy * sumy;

            double sq2 = sqrt(sumxsq + sumysq);

            if (sq2 > 255) //Unsigned Char Fix
                sq2 = 255;
            filteredImg.at<uchar>(i - size, j - size) = sq2;

            if (sumx == 0) //Arctan Fix
                angleMap.at<float>(i - size, j - size) = 90;
            else
                angleMap.at<float>(i - size, j - size) = atan(sumy / sumx);

        }
    }


    return filteredImg;
}

I tried chaging the type of the original image but that just made a mess...Im really stuck please help