By building the curve badly, I mean these things: Did you use the correct degree curve to fit the job (1st, 3rd, 5th, 7th degree etc), did you place your CV's uniformly, did you check your curvature in every view port to check for severe curvature channges, did you use the curve editing tool to achieve tangency, did you use the project tangent tool to get tangency with a surface, did you tweak the cv's pixel by pixel to achieve tangency. There's a great deal involved in building a simple curve that is going to be the basis of your surface. Take all the time in the world to build the curves, because they are the foundation of everything you build.

The square tool has better tangency options than the boundary tool. Really, you could get away with never using the boundary tool.

Here's a visual example. Look at the two top curves. Visually they look almost identical right. Now look at the cv distribution of each curve underneath. Way different!! The top curve was made by making a perfectly straight horizontal curve and pulling the middle two cv's upward. The bottom was made by freehand clicking along the shape of the curve to try to match the shape. These two curves are going to produce two very different surfaces. That's what I mean about building every curve correctly.