Placental Position: posterior to OS

At my 20 weeks scan OB said 50/50 chance it will move..!

OK, what are my realistic chances that this placenta isn't going to cause me issues??? I have another scan booked in for 34 weeks to see if it has moved enough! The only bit that scares me is the "if you get bleeding you'll feel like you wet yourself, come into the hospital".....AND "possible bed rest" .... Oh I hope it moves away enough! What is everyone's thoughts/experiences with this.

I'm not sure how much it's covering.. on my pregnancy summary it just says "Placental Position: posterior to OS".

OB has also advised no running, jumping or bedroom funnies!...