If you have placed a MARKET order, the only element over which you have no say is precisely the price: your order has mandated the exchange to fill your desired amount, regardless of the price and the actual liquidity on the order book. This can result in:
the execution of the order in tranches, with different prices;
the execution of the order at prices other than spot and mark price.
For an exact control of the execution price, please use a LIMIT order.