Sonoline B Doppler question.

So I am curious how much a persons weight effects the usefulness.

I am 5'2" and appox 210lbs I am 13w5d and I keep trying to use the doppler but have not been able to pick up the heart beat with it yet. I only got it on Saturday. I had an ultrasound last Monday and all was good but I have since ended up with Covid and I am starting to get worried. I am not sure if it is my extra poundage or if I should be concerned. Anyone with any insight or similar experience?