I'm not a smoker and never have been so i dont understand what your going through but atleast you care enough to try and quit and you've cut down, thats still better than nothing and more than alot of preg mums do.
I'm proud of you for cutting down and trying, don't beat yourself up over it, lots of ppl (my whole family included) smoke and they still have healthy babies. All 3 of my sisters smoked throughout both of their pregnancies and they all had healthy babies, and unlike you they didnt make the effort to cut down or quit.
Push for your u/s, what matters most is what you want, its your pregnancy, your body and your baby.
Good luck sweetie and all the best