wait are u using a market or limit order? if you want to buy at the current ask price use a market order and it should be filled asap, although if you are buying more than available at the current ask you will pay more for the remaining shares, you could also place a limit order slightly higher than the current bid price to make you offer the best a seller could get at the moment to try and get him to settle for your price not his (assuming nobody has placed a market buy order)