You need to get out of town! Your cake, design, color selection, and construction look spectacular. We'd certainly give you the blue ribbon! Don't let this discourage you. Keep making your beautiful cakes.
It sounds like you've gotten it figured out, which is great. I just wanted to add that I often make a lemon filling using instant jello pudding and add only 1 cup milk. Whip it up and you get a custard-like consistency. It's very good, have not had to worry about refrigeration, and get lots of compliments on it too. Just an option for a simple and delicious filling. (Can be used with any pudding flavors.)
What about adding some curling ribbon (red, white & black) to the upper corner? Seen it done on some sheet cakes here & looks really cute (Cakery did one for a baby shower cake). That might add some color and coordinate with the flag.