Bear in mind that the 300nm is a total, rather than the computed straight lines between target airfields. As long as your log shows suitable turning points and an appropriate duration then it is plausible. IE don't fixate on the first airfield being a set distance from home, work out a sensible way to get there while achieving the requirements. I've had a number of CPL courses recently where the candidate has been turned away from another ATO because their experience does not show straight line distances, but their logbook shows what was actually flown!
In an ideal world, view it as experience building: have a number of flights where you went reasonably far afield during a nice day out, that will make the CPL that bit simpler as a course.