Heartbeat at 8 weeks?!

I bought a Doppler when I was pregnant with my first daughter and it was such a relief to hear her whenever I wanted. This pregnancy I am 7 weeks 6 days and tried the Doppler knowing it might be too soon to hear the heartbeat and I couldn't hear anything and now just very discouraged and scared everything isn't ok. Please reassure me that everything is probably fine! First ultrasound is in one week but I'm overwhelmed!!!