Well first about the organsm,
I've heard (so not necessarily not gospel truth) that when you organsm you cervix actually dips down and contracts almost sucking up the sperm. if that makes sence to you. I've heard that if you don't orgasm during DTD, you should prop you hips up on a pillow or on his thigh and stimulate the outside until you climax. Not letting anything drip out till you do.
And as far as your O date...seriously, I know it's really hard because I'm getting tense about it too, but you really should just relax and let it happen. as long as you keep DTD you'll be fine! And shoud you miss it, you can try again next month.
I know you're probably like

yeah whatever...but if you relax it will help you to not delay the O date. If you stress about it, you could be delaying it.
GOOD LUCK! And happy BDing!