Having an open limit order will place a hold on the associated funds, thereby preventing you from withdrawing or placing another order with these funds. For immediate access to your BTC or ETH, you will need to cancel the existing open limit order you have placed on the exchange.
You can cancel an open limit order at any time. Please navigate to the order book that the order was placed on (e.g., BTC/USD,ETH/USD, or BTC/ETH) via the ‘Buy’ drop-down menu on the Gemini Dashboard. Under the order book display portion of the page, you'll see "BTC/USD Open Orders," “ETH/USD Open Orders," or “ETC/BTC Open Orders.” Under the "Action" portion of the table, click "Cancel Order" link next to the order you want to cancel to cancel your open limit order.