Be very careful about using gca, gcf, etc. in your code. I generally only use those when I'm experimenting in the Command Window.
Instead, call nexttile with an output argument. From its documentation page "ax = nexttile(___) returns the axes object." You can use the "Set Properties on the Axes" example on that documentation page as a model for your code, as it does something very similar to what you're trying to do.
