Looks like you're trying to patch the triangular shape right? Can't really tell from the pic but you probably have to split the bottom spline and/or the top spline. It's trying to patch way over to the end of the wing, not at the bend where you want it.
Select the spline, select the point where to split near the bend, then split the spline. If the nice curve goes away, select both of the newly split spline and use the Smoothing tool.
Hope this helps.
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