Extending a C++ array by creating new one and pointing to it

The title of this question might be unclear but what I'm trying to do is write a program that takes an array, say {1, 4, 7}, and turn that array into {1, 4, 7, 1, 4, 7}.

#include 

using namespace std;

void repeatArray(double* arr, int size)
{
    double* newArr = new double[size*2];

    double* ptr = newArr;

    int counter = 0;
    for (int j = 0; j < 2; j++)
    {
        for (int i = 0; i < size; i++)
            newArr[counter] = arr[i];
            counter++;
    }

    arr = ptr;
}

int main()
{
    double* myArray = new double[3];
    for (int i=0; i<3; i++)
        myArray[i] = (i+1)*2;

    repeatArray(myArray, 3);

    for (int i=0; i<6; i++)
        cout << myArray[i] << endl;

    delete[] myArray;
    myArray = nullptr;

    return 0;
}

The above code outputs "2, 4, 6, 6.95327e-310, 6, 6". It should be "2, 4, 6, 2, 4, 6". Any suggestions on what's going wrong here?