I’ve done this twice, you will definitely need to produce some sort of documentation for the FAA when you apply for your repairman’s certificate.   You will also need a some sort of build log if you ever try to sell the airplane. Since you didn’t keep a separate log, you might just go through the build manual and mark notes on the various pages ie.  “Assembly completed per drawing”, etc. include pictures of some of the completed assemblies from your airplane like the canopy latch, battery box, rudder pedals, etc. as examples of your work.  In this way the build manual will also act as your build log and make recreating your build experience a lot simpler.

FWIW

Jon