Is there a concept of mixed hybridization where bond angles in a hybridized molecule are different angles?
You have to keep in mind that hybridisation doesn't really exist, its just a convenient way of explaining how x orbitals can form y bonds with a certain geometry even though the constituent atomic orbitals point in wildly incorrect geometries.
Take sp3 hybrid orbitals as an example, we combine s, px, py and pz to get 4 sp3 hybrids which we consider to be in a tetrahedral arrangement (i.e. bond angles of around 109.5).
Most molecules deviate (in some cases significantly) from these values, and we can explain that through a variety of steric and electronic effects. The carbon centre may still be considered sp3 due to the orbitals, even if the geometry doesn't exactly match what you'd expect.
Within various hybridisation states, theres also a situation where we would say that a centre has 'more s-character' or 'more p-character', for instance if you consider the bond angles of NH3 vs PH3 and keep on going down, the bond angles change progesively despite them all having the same hybridisation state.