what is most likely to happen if your blood thins out very much

If it thins out too much it wont clot and you would bleed to death.

if you start bleeding it will not not stop because its so thin

you do not want to overly thin the blood or you could have potentially life threatening bleeding complications.
your blood wont clot and a small cut could cause you to bleed out.

Your blood doesnt actually get thin its clotting capabilities change. This is useful to people with artificial heart valves and those who have had blood clots and heart troubles. If you overdose on Warfarin/Coumadin you may risk an internal bleed or you may just take longer to stop bleeding from a cut.