Mono/di twins mistaken for di/di

Hi everyone! I had my 24 week ultrasound today and thus far my pregnancy was categorized as di/di. Today it was confirmed that it is actually mono/di. My husband and I are frustrated that it wasn't caught sooner and have an OB appt. on Thursday where we plan to ask a lot of questions, but just wondering if we missed any important tests or precautions along the way. Being that it's finally been corrected at 24 weeks, we worry that there are things we should have been doing all along. Would love to hear from other mono/di mamas and appreciate any help.

Thus far, we've had ultrasounds and OB appointments every 4 weeks, I take a prenatal every day as well as two 81 mg aspirin and make sure to get lots of rest.