OpenCV cv::Mat element access

cv::Mat matrix= cv::Mat::zeros(3,4,CV_8U);
matrix.at<float>(0,0)=1;
matrix.at<float>(0,1)=2;
matrix.at<float>(0,2)=3;
matrix.at<float>(1,0)=4;
matrix.at<float>(1,1)=5;
matrix.at<float>(1,2)=6;
matrix.at<float>(2,0)=7;
matrix.at<float>(2,1)=8;
matrix.at<float>(2,2)=9;
for (int i=0;i<matrix.rows;i++){
    for (int j=0;j<matrix.cols;j++){
        float temp= matrix.at<float>(i,j);
        std::cout<<temp;
        std::cout<<" ";
    }
    std::cout<<std::endl;
}

Excpected output:

1230

4560

7890

Current output:

1478

4789

7890

Что не так?