Ideally you would have the dozer guy come back and do that job. He can dig the clay from the shallow end and push it to the spot that needs covering. He can also pack it really well with the dozer. Probably a couple of hours of work, no more than an afternoon. Next time he is moving his dozer have him swing by and fix it...before the pond starts filling. Better safe than sorry.
With other ponds in your area being successful, once you fix that sandy area, you should be good to go...assuming he has done a good job applying clay everywhere it is needed.
