I think the reason those French were on the Belgian border was the 102,000 stack you stationed there. I think if you move forces away from the border they will also. Also you might want to give them mil access so they can attack British interests through your territory. You can always rescind it later. Doesn't matter now though, might in the next war.
I too have made that WP accidental accept mistake before also. That's why I don't even bother opening the dialog until I'm ready for peace. I figure that in the heat of battle you don't want to do break routine making automatic reflexive clicking on dialogs unless you're sure what they are, so don't bother until you want peace anyway. Also, I usually burn one of my DPs on peace deals instead of clicking on their offers just to make sure I get everything I want and that I don't make mistakes.