Hello - you do need a referral for a Scan and this is not likely to be done at the antenatal appt. As the others have said I would call and book in for the scan and then get the referral for the blood test and the scan if you want it done. The timing is important and the scans can get booked up. You could also call ahead of your appt to talk to the midwife/Dr about this as if they are only seeing you at 12 weeks you may want to arrange it earlier. It is not always offered (esp if you are quite young/low risk) so they may have overlooked or assumed you did not want this.
In terms of what to expect at the appt, i think they will all be diff. I am seeing a private OB so mine may not be the same as yours - but I had a breast and heart check, BP checked, weight (she does this only at beg), spoke about hosp, birth options etc etc...