low HCG

I got my 15dpo/15dpiui beta levels back and have been a nervous wreck ever since. The nurse from the fertility clinic said that my levels were "very low" at 45 and that they should be above 100 at that point in time. I'm going back for another beta tomorrow morning but I don't know how to quell the nerves. I'm terrified of having an ectopic or chemical pregnancy. My husband and I have been TTC for so long now and I was so thrilled to see the second line on the pregnancy test at 11dpo. Any words or wisdom? If anyone experienced this, how did this turn or for you?