HR inaccurate

I am a new Venu3s user. I have another HR tracker, a BP cuff, and a doctor spouse who can count my HR very accurately. Unfortunately, despite following fit instructions, my watch seems to be always off when I am standing or walking, which is when I need the HR monitor most (I have a neuroimmune disease). I am about 3 days into using. I am wondering, does this get better? Or is there something I might have done (ex setting my HR max too low due to my condition) that would have impacted this seeming miscount. It is most noticeable when walking around.