The ship icon orientation is dependent mainly on two things.
Of only GPS-COG is present the ship icon is following that.
If a heading from a compass
is present the ship icon is pointing according to that course even if the COG is to another direction.
Check your data flowing into OCPN for a heading, e.g. HDM, HDT. If for example you have a heading turned 180° the ship icon will be perpendicular to the COG.
The prediction course line and heading line appearance are set in Tools->Ship->Own ship.