CAS Schedule

I’m confused. Nung ngpacheckup ako last May21, binigyan ako ng OB ng request for scan for June 15 onwards, she even recommend a hospital where I can do my CAS. So i contacted the hospital to have my CAS schedule, they are asking for my current week so sabi ko based from LMP going 20weeks nako... and for the last ultrasound naman, i also mentioned na going 19wreks (magkaiba kasi). Tapos sabi nila hindi pa daw pwde ako iCAS kasi dapat 22-26weeks daw. Pero may request kasi ako from OB. My question is should i proceed with the CAS even 19/20weeks pa lng ako? And if yes, june15 onwards sabi sakin but they have slot din this jun13, ok lng ba mas maaga ng 2days?