I don't have your dataset but you can follow this example:
plot(3:10, (6:13).^2, 'k.-', 'LineWidth', 1.5)
Rsq = 0.64645;
h = gca;
pos = [h.XLim(1) + 0.1*diff(h.XLim), h.YLim(2) - 0.1*diff(h.YLim)]; % top left corner
text(pos(1), pos(2), compose("R^2 = %.2f", Rsq))