Your first point broke because you put enough pressure on it to cause it to flex.  I suspect it was too steep an angle.  Some times, you have to "nibble" those thick spots down until you get the right angles to run a long flake.  You want to push almost straight in, parallel  to the width on the point.  
I also agree with Tower, you are moving into pressure flaking a little too soon, you needed to whack a couple of those preforms a couple of times to get the high spots off.
Your second point looks pretty good, keep after it, you are starting to get the hang of it.  Bill