Mild contractions and didn’t know?

Had an appointment today with my obgyn and when I laid on the table with my shirt up so she could measure my stomach, she took one look and told me I’m having a mild contraction right at that moment and told me to feel my stomach and it was so hard. I never knew that was a contraction? Why do I feel so stupid for not knowing that.... now they have been happening all day. I’m 38 weeks. Anyone else never know what a contraction would feel like and was clueless when you started to first have them? I also wonder if that means labor is close. I should’ve asked. Ugh 🤦‍♀️