Better to redraw...seems you have overlaping curves ;)

- Draw the box
- Draw the external outline on the box (Rectangle + Fillets)
- Draw the internal Offset
- Boolean Diff Box / Internal Offset = Solid 1
- Draw the arc curve Profil
- Sweep
- Planar the "Offsets" (for security to see 2 solids...)
- Join the 2 Surfaces = Solid 2
- Kill curves
- Boolean Union Solid 1 + Solid 2 = one solid :)

With training in less 60 seconds you will keep your hairs! :)

It's that i made...no special problem! :)