When your instructor endorses your logbook for the X-country, he/she is saying that you have the ability in his/her professional opionion to successfully complete the mission.
They call it a "checkride" because the examiner is just endorsing the instructors opinion that you are in fact the rating the instructor says you are. Or, to put it another way, until you fail the checkride, you are the rating the instructor signed you off for. That is why it is called a "checkride" not a "final examination."
Hope this helps. (And gives you confidence in the system, you can do it!)