Almost 17 weeks

I bought a fetal Doppler but I'm still terrified I don't know if I am using it right I have heard the baby's heartbeat and I have started how about if it's not what I think it is I don't have ultrasound appointment until June 25th and I don't have a doctor's appointment until June 27th I am four months in my second trimester almost 17 weeks last appointment that I had with a doctor was May 30 and I heard the baby's heartbeat it was 142 and before that May 14th I had a ultrasound and the baby was fine heartbeat then was 158 the baby was upside down when will this feel go away of being terrified I know the baby is fine but I'm still terrified I don't understand why everything's going to be fine everything is fine anybody else feel the same way I feel