In other words, is it surfaces and then a subsequent thickening.
In my opinion , to start with, try to drag the blue dot from the top to the tip to the right.
But in my opinion and given the shape I would be surprised if you could make your case in a single smoothing in pure volume with a single point connection (without going through the surface).
Let's wait for the surface specialists to tell you how to do it!
Can you post your piece while waiting for me to take a closer look at your model.
I'm working on the 2018 version. Attached is my document file.
The fact is that I managed to retrieve a file from the Internet modeling a similar shell that used the boss/smooth base function. I don't understand why I can't do the same on my sketch...
I think that you should first make a surface rather than a volume, it will be easy to make the 2 flat surfaces of closures necessary to obtain a volume. We are on basic surface that does not require any particular knowledge, it is the same logic of use as volume.
You would have to see the shape (open/closed) of the different sketches (I don't have 2018 at hand).
I just opened your file, I didn't have any particular problem generating the surface.
Note that in surface you have to be careful where you click on the sketch, this is what will determine the position of the green control handles like in my image.
So click on the end of sketch 1 and then 2 where I put the arrows. So the 2 green handles are on the same side. If not, the surface will twist, but just slide the green handle to the opposite side.
then the guide curve . and validate.
By the way, having done naval modelling in wood and under SW, you need a lot more guide curve that I have represented in orange. and ideally it would be necessary on the horizontal plane too but it becomes more complicated to match everything.
It's a good thing I found what I had done 12 years ago :p but I had stopped for hardware limitation at the time.