Wow, some of the judgment on here.. I guess it's not surprising that most reluctant women are to be honest about drug and alcohol use at any point in their lives, particularly when pregnant, despite if they didn't know. People come on here and judge you as if they have lived lives without any shame and regret, picking apart your post like they know you. At least OP stopped once she found out and is trying to get help. Why jump to the assumption that she is lying? It's stupid..
@Kakaka1 , nobody knows if your baby will be affected or not, nor will any consultant or midwife. And, like most things in pregnancy, you'll have to weigh the risks and decide for yourself what steps you take from here on out.
Don't let anyone tell you to terminate based on their own experience, and likewise don't let anyone tell you to lie about your consumption. Educate yourself and make decisions based on what feels right for you and the baby. You can't change the past. It's about moving forward now.
We all make mistakes, try and get help from a less judgmental environment (dedicated support groups and nonprofits, a professional with experience in this area, NOT mumsnet) to help you get through the pregnancy, should you decide to continue it, as it will likely continue to affect you even more further down the line. You'll need extra support.
Be honest with yourself and your medical team. They might recommend things like additional scans, a healthy diet and exercise routine, an amnio in your 20th week, and other things to make you more informed and to increase the chance of a good outcome. Best of luck. x