Working out the area of a spline loop, do I need to use shoelace formula and 2D projection?

I’m a bit noob when it comes to maths so I made a shape and used the blueprint above for the area calculation. The area is in the middle there. Is this the correct answer?

If not I think maybe it’s inaccurate.

The numbers are:

278.847 (left)

230.308 (right)

361.694 (base)