I took next choice about three weeks ago and now I'm 6 days late on my period should I be worried?

I'm assuming that this is some sort of morning after pill?

If so, they can and will throw off your period.

Having said that, no form of birth control, and no form of morning after pill, is 100%. There is a chance that you could be pregnant. Wait until your next period is due. If you miss it than test using first morning urine.