But it is better you should try and contact their customer care than doing nothing about it.
Just do not use more than $100 to gamble on the site for now. You do not need to deposit into the site next week or next month. Be using the money in the casino instead of depositing more money. Do that until the weeks or months you would have deposited $1000 has been reached.
I believe that the OP's problem is precisely the need to use the excess $900 for other purposes that exact month, such as paying bills or shopping at the supermarket.
Be aware that the OP deposited 10x more than he intended, which is no small feat, regardless of the amount he is referring to.
I have always believed that all casinos should require their users to first open a deposit order on their website before initiating any transfer, typing in the exact amount they want to deposit. If anything more is transferred to the casino account, it should be automatically refunded to the customer's checking account, wallet or credit card. The casino could hold at most the transaction/refund costs necessary to return the excess amounts.
This way, users can rest easy without worrying about errors and casinos also do not need to worry about money laundering, since the entire amount would be automatically refunded to the same account that made the deposit.