Call me crazy, but I always thought the best way to plot a circle was PolarPlot(1).
Here's a more general kludge of a way of plotting equations of the form x^2+y^2=1:
data = @[135, 135]
for [row, column] in data
x = (column-68)/60
y = (row-68)/60
data(row, column) = abs(x^2+y^2-1) > 0.05
It's crude, but it works. Adjust 0.05 to alter the line width.