I'm a bit envious of someone feeling like they needed to grind. I did every single sidequest I could find so I was overleveled for most of the game :(
That's why the inn system exists! It's specifically designed so that you can do as many side quests as you want without applying the EXP you earn to your party.
Unfortunately you can't de-level yourself if you use your bonus EXP and then change your mind later. You can only do that in NG+.