The way you write make is seem like you've had BMXes before.
One easy option is simply that this bike has another gearing ratio than the ones you're used to. Harder to get going, more top speed before spinning out.
Count the teeth, front and back, and compare.
Apart from that, as OH says, unless it's a really obvious and easy fix, like a wheel sitting crooked in the frame and rubbing, bring it back and let the shop deal with it.