It is possible you will need a new flange. More likely your floor/tile are uneven, in which case you need to shim one side or the other with a vinyl shim, then caulk the gap.
what country r u in if in belfast , The Yard is the best for toilets with fixing bolts for the pan . but if u can jus buy a toilet an u only hav to use 2 brass screws for the pan and 2 normal screws...
This will involve removal of the toilet from the floor. You will need a new wax seal kit which comes with new bolts. The bolts are actually attached to the top of the receptacle ring in the floor....