i miscarried in july 09 and just checked my babys heartrate on my fetal heart monitor and it was 172, yay.......i think you will be okay, just relax and maybe buy a dobbler to ease your worries! HERES THE WEB SITE I GOT MINE FROM
http://cgi.ebay.com/FDA-Approved-Baby-Sound-B-Fetal-Doppler-Free-2-oz-Gel_W0QQitemZ370284367860QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item5636ab0ff4
im 19 to :), congrats on your pregnancy! and anyone can really miscarry, but i wouldnt worry about it though.. my sister had a m/c in august and then she is pregnant again with a healthy baby lol so just relax :) and good luck!