2nd opinion?

I have been having spotting and contractions for 2 weeks (we saw the contractions on the US, so I know it's not round ligament pain) so my midwife did an US and measured my cervix at 2.5cm at 16w 6days. She is a very natural, relaxed lady and told me just to rest and stay hydrated. I am concerned about it being 2.5cm this early in. Anyone have experience with this? Should I get a 2nd opinion or am I overreacting? Thanks!!