elevated HCg

Clare
Hello everyone.  At 9 weeks pregnant I had blood tests which revealed an elevated hcg level. Doctors said I was probably further along than I thought but according to my dates and my ultrasounds I'm right on track n there is just the one baby in there. 
I'm wondering if anyone else has had the same n what problems can the heightened level indicate?  This is my second baby and from memetic this is the first time I've had these results.  Should I be worried or no?