"I am in california i have the same problem new lawn planted in late
august
in the shade planted sun shade lawn seed but it does not get bushy?
what to
do with lawn "

Well to start with, since it's shade, I'd plant a mix designed for
shade, or dense shade, not an all purpose sun/shade mix which is a
compromise. Depending on how shady it really is, fall may not be the
appropriate time to seed. On the north side of a house, for example,
with the days growing shorter, and the sun heading south, it will get
very little sun now. That type location is better to seed in the
spring. What's the soil like? Has it been tested, PH adjusted? Did
you keep it moist for several weeks?