It should be an upside-down ("sad" face) curve, all because of that negative sign outside.

Also, in your working, the negative sign should only be multiplied to one of the brackets (either to x - 8 or to x + 3, but not both at the same time)

The y-intercept value will be 24 instead of -24.

If turning points are needed, (2.5, 30.25) or (5/2, 121/4) will be the maximum point.