I have a design that I have created, but one end of the model is flat compared the curvature of the rest of the model. The end with the fin is meant to be flat and is corrrct, but the other end doesn’t follow the continuity of the curve and I am having trouble attempting to smooth this out. Any help is hugely appreciated, hope this makes sense! 
Also, I don’t know how to attach the shapr file as I am still a new user.
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have you tried the Guided Loft tool?