It’'s a common problem because, unless you spend a lot of money on professional hardware, the absolute speed of camcorder / computers / sound recorders … are not very accurate. Perfectly good enough on their own, but problematic if you want to synchronise 2 or more devices.
The workaround is to give yourself timing points at the start and end. A “clapper-board” is ideal, but almost anything that is both visual (for the video) and audible (for the sound) and “sharp” (for precise timing) will do. Then there is this plug-in with which you can stretch the audio to match the length of the video: https://forum.audacityteam.org/t/change-speed-stretch-audio-to-a-specified-length/23332/1