How to fix this (model had weird angles)?

I’m working on my first blender model. It is an armor prop shin guard based of a animated character. I’ve gotten to the point where I have the shape I want, but its not very smooth. There are weird angles left behind that are very apparent when 3d printing.

I’ve tried using sub divide smooth, but this makes things round it seems (and why is it that some faces don’t subdivide but others do?).

The way I created this (maybe the problem was how I created it?) was to take the shape of my leg (created in Rhino3D), did a face select to get the general shape I wanted, duplicated and separated out the selection. Then I worked on that until I had the exact shape I wanted. I duplicated that again, did a “inset faces” command to make the outside edge. I cleaned up the result of the inset face, and moved it around to try to match perfectly with the base shape. I then solidified both and boolean unioned them.

The weird angles showed up during the solidify step and I haven’t been able to figure out a good (fast?) way to get rid of them. I’ve tried deleting specific faces and remaking them but I get similar results. I’ve tried using smooth in clay edit mode but I don’t think I understand how that is supposed to work cause I don’t think its doing anything.

Here are the pictures:

This is the actual model it its current state. There are two holes in the faces on the back section of the shin guard. I’ll fill those in but haven’t done it as I figure I’m going to have to delete half of it anyways to apply another mirror modifier.
HectorShinGuardv1.2.6.blend (1.45 MB)

ok i know this is an old topic but i took a look at the model and the topology is (no offence) horrendous. you have ngons all over the place there causing the shading to come out like that. allot of unnessasary shapes in that area that could be removed and have the same effect after.