Is 88 bpm a low fetal heart rate at 5 weeks 6 days?

I am 6 weeks pregnant today..I went to the dr 2 days ago(5 weeks 6 days) i seen and heard the heart beat which I was suprised by bc i am so early. The doc said that the heart more than likely just started beating that day or the day before..but the hr was only 88..this is making me very nervous that it is to low..the dr said everything looked good but has anyone else had a fetal heart rate this low in the beginning? How fast does the heart rate increase? This is my first pregnancy so ive been a nervous wreck about it. Shouldn I be worried or is this normal! Any feedback is appreciated.