ultrasound question

Is it wrong of me to double check with my doctor to see if I can do an ultrasound earlier? I had one done at 6 weeks because I have a history of molar pregnancy but my next one isn't until 20 weeks. I just don't feel comfortable with that huge time gap. if it sounds like a dumb request I'm going to look for an independent ultrasound studio. I want another done around 14-15 weeks