Just in case anyone is having this issue,
if you make a .reg file and put it on your desktop you can change your sens back quickly in case you need to change ingame settings. The game will respect registry changes midgame, so you can change graphics settings, etc. and then run the .reg and get your sens back.
For example, what I have set up is
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\SOFTWARE\IronGate\Valheim]
"MouseSensitivity_h2921938665"=hex(4):00,00,00,c0,60,e5,00,40
Replace the red letters and numbers with whatever sens you get in the calculator.