Add packing tape to the leading edges. You can also bury carbon fiber rods in the underside, but that's a major undertaking. Gluing or taping thin (3mm square) spruce strips to the underside may help. Even balsa probably wouldn't hurt other than the weight penalty.

Here's the harsh reality. You have a model with about a 1 meter wingspan. The real 182 has 36 feet of wingspan, or about 11M. A 10 mph wind to your model would be like a 110 mph wind to the real airplane. A good full-scale pilot in those conditions would probably do no better than you are doing.

Sorry, I really don't mean to be cruel but there are some harsh realities that have to be worked around.