Baby Doppler- question

I am 10w1d along with my first and my baby Doppler came in today I was so excited but I knew it might be a bit frustrating trying to find my little ones heartbeat. After 20 minutes of trying i hit a spot beside my belly button and the screen read 174 and bounced to 178 but then I totally lost it. Do you think this was the heartbeat or maybe I moved too fast and there was an error? I heard what I thought was that train noise rather than my heartbeat but I don’t know. Any advice?