Matplotlib heatmap is really small

I have created a heatmap that will display the correlation between all of the columns within a dataset of random numbers. The heatmap is created just fine, but the heatmap is very small, mostly in the vertical direction. I attached an image of the heatmap to this post. The dataset is a pandas dataframe from a csv file. The code is shown below:

def colCorrelation():
    xData = []
    yData = []

    fig, ax = plt.subplots(figsize=(5,5)) 
    # calculates the correlation between all columns and all other columns
    for i in range(0,100):
        for e in range(0,100):
            dataFlow = dict(zip([(i,e+1)], 
               [np.corrcoef(dfT[i],dfT[e+1])[0,1]]))
            if list(dataFlow.values())[0] < .9:
                xData.append(list(dataFlow.keys())[0][0])
                yData.append(list(dataFlow.values())[0])

    ## tuple of the two columns being correlated and their correlation
    ## in the dictionary as key value pairs data structure.
    ## Ex: {(19, 17): -0.015262993060948592}

    ## Plot heatmap
    heatmap, xedges, yedges = np.histogram2d(xData,yData,bins=(50))
    extent = [xedges[0], xedges[-1], yedges[0], yedges[-1]]

    plt.clf()
    plt.title('Random Data heatmap')
    plt.ylabel('y')
    plt.xlabel('x')
    plt.imshow(heatmap,extent=extent)
    plt.show()

colCorrelation()