I'm 34 weeks pregnant, and measuring 30 cms! I'm so scared!?

I just went to my 34 week doctors appointment today and everything went good as usual, although I've attained a bladder infection which is fairly normal throughout pregnancy. I got a prescription for amoxi and it'll be taken care of in a week hopefully! My little boy kicks day and night, hiccups, and I feel his movements low and high, so from the outside, I feel that he's healthy. My doctor measured my uterus today and I'm measuring 30 cms. The usual for around this time would be 34 cms, and it has me really worried. Although she's really calm about it, she's scheduled me for a fetal assessment to make sure everythings good with him. This is my first pregnancy and I worry about everything, as you can see from my other questions lol... If anyone knows anything about this or has had some of the same experience, could you share them to calm my worries? thanks!