Several issues with regards to the compression test:

All sparkplugs MUST be out.

The throttle plate MUST be wide open.

AND-- you need to have a battery charger connected for consistency.

The test isn't really valid with 1 plug still in.

Forget the bore scope, in the time it takes you to go get one, you can have that last plug out.

Happy to help, I am a mechanic with 30-years experience.

Brad

btw, where are you located?