I have spent a couple of days troubleshooting this and have had no luck. Below is the project I'm working on. It is a fin for a wakeboard and needs to have curves in 3D.

The issue I am having is when it comes to the two tips of the fin. The majority of the surface is a lofted surface but that cannot extend to the tips. I have heard bounded surfaces would not work because there are only two edges and the grid system used does not work with that situation. As result I think a filled surface is best but that is just one of two issues. My first problem is that my surfaces do not follow their boundary curves and leave gaps. Here is a view of the bottom surface (blue

being curved top surface) where the filled surface I used fails to follow the boundary. The boundary IS symmetrical but here is another example where the lofted surface

does not follow it's guide curve. Notice how one side follows pretty well while the other is no where close. This is a top view looking down on the part.

The second issue and I think the larger one is using filled surfaces. Here I re did the part so that it was only half and extruded the top edge to give a nice reference to be symmetrical about

I next selected the three edges on the tip to form a filled surface and created tangency relationships to the top curved one and  curvature to the side curved one. I then made the bottom just a contact relationship. The results are close but with two large bulbs instead of following a curve that I want as shown.

adding another curve similar to the side curves that I lofted to make the existing face only puts a valley in the bulbous surface and does not fix my problem.

I have attached my part made on SW2016 if anyone would like to play around. I hope someone can find some joy in my frustration and take on the challenge! Thank You.