They always measure me less and try changing my due date, but I know I measure small so I just stick to my original one :D
Yea, nothing to worry about. Those measurements can be off by a few weeks. Doesn't mean anything really. With my first pregnancy I measured 2-4 weeks ahead the entire pregnancy and this pregnancy I've been measuring smaller the entire time. Just depends on baby's size and also the position of the baby when they are measuring you or amount of fluid you have. It's not an exact science really.
Those measurements that they give you are just a guideline, every woman measures differently. Some are less and some are more. Keep us updated on your pregnancy :)