I know it's been a while since this thread has been touched but I thought I'd give a little input. Your length is really large, and it would be hard for the woman to take the entire length. There are positions you can try to make this easier, you'll just have to look it up.

The good news is that your girth isn't something that should scare away women. My boyfriend is way endowed (not 12), but his girth is quite large (just over 5 and a half). This at times can make me very sore but your girth is something a woman can handle. I suggest investing in a doughnut c-ring. It'll make it easier for her to handle all of you and hopefully give you better luck. I hope it works out.