We only accept market orders, which are orders that are immediately executed at the current market price. Keep in mind that once an order has been filled, it cannot be reversed.
There might be cases where your order is not completely filled. For example, if you place a huge order and the stock is thinly traded, there might be a partial execution. If this happens, your order will remain open until there’s enough volume in the market to fulfill the remaining shares of your order, or until you cancel it. If the latter happens, you will keep the shares that were purchased.