Hybridization of orbitals

I dont understand how sulfur in sulfur trioxide hybridizes. I know that it needs to hybridize from 3s2 3p4 to obtain 3 sp2 orbitals and 1 normal p orbital. I understand that 2 of the sp2 hybrids are for the single bonds with 2 of the O's, and 1 sp2 hybrid and 1 normal p are for double bonds with 1 of the O.

What I don't understand is this: the 2 of the sp2 hybrids involved in single bonds with the 2 O's won't be filled because it will form a coordinate covalent bond with O. Would it make a difference in terms of the way S hybridizes if it were to form coordinate covalent bonds? Can anyone explain how the S hybridizes?