questions about miscarriage

I am currently 6 weeks pregnant and freaking out that I might miscarriage. I was diagnosed with endometriosis about 4 months ago told I would have a hard time getting pregnant then on Christmas I had a positive pregnancy test. I have been to the doctor and in the ultrasound because I was in a lot of pain but come to find out it was morning sickness. They saw the baby's heart beat and heard it at 104 bpm. I got a call from the doctor though saying that the baby still hasn't attached in my uterus though so there's still no guarantee it will be a viable pregnancy. So I want to know when I can stop freaking out and feel safer about this pregnancy? Thanks guys!