just a little pregnancy worries

I went for my monthly baby check up on Saturday. I gained 2 pounds, so that puts me at losing only 2 pounds so far this pregnancy. I am officially 19 weeks today. Almost half way there...I have an ultrasound scheduled for Tuesday, March 25. CAN.NOT.WAIT for that...I am so excited to finally see this baby and know that the baby is healthy and also of course find out what this little baby is Pink or Blue...
The doctor does have me a little worried though..She said I was measuring bigger than I am week wise. I guess when your prego your belly should be the number of weeks you are, I am 19 weeks and my belly is measuring 24..I asked her if there was anything to worry about and she said probably not but to go ahead and schedule my ultrasound for about 3 weeks from now...Well I did that, but I'm still a little nervous because she didn't give me a yes or no answer. I am confident in my doctor though and with both pregnancies before she is always very cautious. So I am okay with waiting the 3 weeks until I am 21 weeks for the next appt. I know that if she thought something was wrong she would have given me an ultrasound right then..Shes like that.
I read somewhere that some women can be more cautious with there 3rd pregnancies because they already have 2 perfect, healthy children at home and only wish the best for the next child..I think I may have that problem. I am way more cautious, and careful with this baby than when I was pregnant with Hannah and Alanna. So wish me luck and mark your calenders to come check out the news on March 25...