I recently bought FT Might mini Corsair and the first few times I flew it, the plane held in air but then started to swerve to one direction. I have the custom "power pod" angled differently and I think that might be the answer
Also is there anywhere I can get 6x4.5 propellers.
Apart from the usual geometry problems possible with a build the thrust angle of the motor/propeller can cause swerving to the side.
For a ccw rotating propeller right thrust is required to stop a tendency to swerve left though too much side thrust can cause it to swerve right. For a cw rotating propeller left thrust would be required.
The problem is most apparent at low speeds and full throttle so launches at half throttle with a hard throw will give a safer launch and time for the plane to gain enough speed for the controls to overcome or override the turning tendencies.
As for your request for a supplier of the 6x4.5 propellers I am sure the FT store could help though I buy them by the bucket load from HK. I use ccw and cw propellers so matching pairs are not an issue for me.