Natural convection in a low Prandtl number, liquid metal gallium was numerically simulated in a 2 mm narrow gap test cell to benchmark experiments. One two-dimensional model and three different three-dimensional models were tested using a commercial finite element code and compared to an X-ray visualization experiment. Significant differences were found between the results obtained in the two-dimensional and individual three-dimensional models. The inclusion of the bounding solid walls of the test cell in the three-dimensional model resulted in temperature contour profiles which are comparable to the experimental visualization in liquid gallium.