I also have pcos and so far I have had 2 pregnancies and 2 miscarriages. I am not sure about the lining but I imagine if you get pregnant on like a 40 or 50 day cycle the lining could be overgrown or inhospitable. Both of my pregnancies happened on longer cycles and my RE said there is some thought that if you ovulate many days past the normal 14 days, it is possible that the egg is "geriatric" by the time it is fertilitzed and that can lead to m/c.
There is no way to tell really if you will m/c, I just wanted to say that I have PCOS as well and I have been ttc for 3 years (me 24, dh 25) and I have done six cycles of Clomid-no luck. I went to the RE found out I have PCOS and was put on Femara. Anyway women with PCOS are automatically at a 50% chance of m/c, and Clomid does thin out uternine lining. Best wishes hope this helps a little and your journey is quick!