Hi there!
We converted our daughter to a toddler bed about a month ago, when she was 19 months. We went through her getting up every night at about 4:00. She would then bang on the door and eventually sleep on the floor behind the door the rest of the night! We went through putting her back in and in, and in, and in, and sleeping on the floor many of nights, but now, finally, she stays in all night. One thing I did was change her sheet to a really comfy, flannel sheet. This seemed to help. If you don't have one, you can just put a really soft blanket around the mattress.
Is there anyway you can shut his door or could he still get out? My brother had to put a child safety thing on their daughters doorknob so she couldn't get out!! (There is a small element of danger to that, though). I think the biggest thing is routine. If he gets in the routine of sleeping with you, that is going to be the norm. That is what he will think is right. It is sometimes nice to cuddle with them, (especially when they go a million miles an hour during the day), but you have got to put your foot down and get up and put him back in his own bed. This may take a couple of nights of endless putting him back and lack of sleep for you, but it will be worth it.
Anyways, no I don't think you did it too early. If you put the railing back on he will still have the idea that he can get out, therefore he may TRY and climb out now, since he could get out of the bed. And like you said, that could be dangerous.
Good luck!
R.