Nearly right potato soup

I made potato soup last night. It didn't come out quite right, but I'm posting the recipe I used and I'll point out the mistake I made. I don't quite know how to fix it yet.

6-8 potatoes, peeled and diced
1/2 onion, diced
2 cloves of garlic,minced
2-4 strips of pork bacon, cut in 1 inch pieces
4-6 strips of turkey bacon, cut in 1 inch pieces
3 mushrooms, sliced
Ground black pepper to taste

2 liters chicken broth
1/2 cup white wine
1/3 stick margarine
1/4 cup whole wheat flour
1 cup ow-fat milk
3 teaspoons freshly chopped cilantro
1 teaspoon dried tarragon

Set the bacon to fry in a soup pot. Before it gets crispy, add the onion, garlic and mushrooms. Saute until the onions begin to turn translucent. Add the potatoes and black pepper and toss them around. Saute for two minutes or so. Add the chicken broth and wine, stir well. Reduce the heat to minimum and let it come to a slow boil. Simmer until the potatoes begin to get tender.

When the potatoes are nearly done, melt the margarine in a separate saucepan. Whisk in the flour. Here's where I erred, by using too much flour (about half a cup). Add the milk and keep whisking. Add the cilantro and tarragon. Make sure you get a smooth, creamy mixture. I got lumps, and those things won't dissolve in the soup.

Add the mix to the soup and stir. Let it boil a second time, simmer a bit. Serve.

As I said, mine didn't come out quite right due to the lumpy flour/margarine/milk mixture. I think using half as much flour, 1/4 cup, should fix it, but I really need to try it. If/when it works, I'll post it again with pictures.