Is it okay if i took 300 zoloft (sertraline) instead of 150?

no: I don't know if you mean once, by mistake, or regularly. If you doubled your dose by mistake once, it's unlikely to be harmful, although you might suffer serotonin side-effects (stomach upset, jitteriness, restlessness). Taking 300 on a regular basis usually does more harm than good. It's not okay if your doctor didn't prescribe it that way.

Zoloft (sertraline) dose: Although zoloft (sertraline) may be prescribed at an off-label dose of 300mg per day that would only be under psychiatrist / physician supervision and if there was not adequate response to a lower dose. DON'T change medication doses on your own.