Short Cervix?!

I’m 15 weeks 2 days today and my cervix is on the shorter side at 33.8 mm 😭 I’m getting SO worried now, but my OB at MFM wasn’t concerned at all… She said my cervix was closed and still at a decent length, and also passed the test where they put pressure on your abdomen to see if it opens up at all.

Everywhere online says it should be at least 35 mm! Anyone else have a shorter cervix before 20 weeks and everything was okay? Should I ask to be put on progesterone?