As others have already pointed out, you need to interpolate your data.
There are a number of different ways to do this, but for starters, consider scipy.ndimage.zoom.
As a quick exmaple:
import numpy as np
import scipy.ndimage
import matplotlib.pyplot as plt
data = np.loadtxt('data.txt')
# Resample your data grid by a factor of 3 using cubic spline interpolation.
data = scipy.ndimage.zoom(data, 3)
plt.contour(data)
plt.show()
