A few possibiities:
First, during excessively hot, dry periods, it's best not to apply herbicides like this to turf. It can burn the lawn.
Second, you don't say what kind of sod you have, but a southern type of grass - bermuda, zoysia, st. augustine - needs weed killer specifically formulated for those grasses. If you used the versions they sell for bluegrass and fescue, you would definitely see some damage.
Third, it's possible you simply overapplied it.
Not saying any of these are definitely the case, just throwing out some possible causes here. All of these are problems that are addressed on the label, so go back and read through it carefully to see if it sheds any light on what happened.
The good new is the that more often than not, lawns outgrow this sort of damage. (just keep it watered)