Ultrasound

Hello I am only 27 weeks and I'm wondering when I get my last ultrasound I want to see my baby so bad but the doctor hasn't scheduled me one yet I've been to the doctor of course my last appointment was on Friday and he listen to the heartbeat he said everything was good but I have no news about an ultrasound... do I have to ask ???

Or is it when the baby is more farther along cuz I'm already in my third trimester and I see the doctor on the 29th of December do you think I should ask ??? IDK

Please answer help appreciate it