I had the exact same situation as you some years ago when I got my JUC ring.
I chose a 52 at the store initially. When I went back home, I did a shake test. Ring immediately just flung off into the far corner of the room!
Immediately went back the next day to exchange for a size 51. 
My fingers may have been more swollen at the time I was trying on the different sizes, so it felt okay at the time, but I am glad I sized down.
Initially the size 51 nail head did dig a little into my finger. But it was not painful or anything and I got used to it quickly.
Hope this helps!
I chose a 52 at the store initially. When I went back home, I did a shake test. Ring immediately just flung off into the far corner of the room!


My fingers may have been more swollen at the time I was trying on the different sizes, so it felt okay at the time, but I am glad I sized down.

Initially the size 51 nail head did dig a little into my finger. But it was not painful or anything and I got used to it quickly.

Hope this helps!