I take 150 mg of Zoloft (sertraline) a day and today by accident took 150 in the am and 150 at night. The reason for the mix up was I started to take it in the am.?

No worries. It is very unlikely you would have any significant adverse effect from accidentally repeating the dose. Zoloft (sertraline) is routinely dosed to 200 mg daily and to 300 mg daily for some conditions including ocd.
Probably fine- Probably will not hurt as a one time event - i would probably only take 50 tomorrow morning.