I think part of the problem is that your outer radius / circular scallop feature is not tangent with the inner radius / scallop feature.

I created, in your file, a similar profile and with a single click, put a fillet of 2 units on the whole thing just by clicking one edge. Since I made my initial sketch with tangent relationships the fillet was able to 'chain' around all the edges in one shot.

If you look at your object from the top view and zoom in close to where the outer and inner radii meet you can see that the outer rounded surface runs out just past the point of tangency while the inner radii comes up short of being tangent. What you will need to do is either make the outer radii the driver and adjust the inner radius to meet tangent, adjust the inner radii as the drive and make the outer radius match tangent or split the difference.

The image attached shows you in black lines, how your profile sketches cannot be tangent....ever. While the red line for the inner radii shows how you can use the outer radius as the driver while changing the inner radius in order to run tangent as it should be.

This isn't a MoI or other program issue but just modeling practice. I have had my knees skinned a few times too but best to learn as soon as possible.