When you buy bitcoin at the price of $9k, you need to wait for the price to increase at $10k or more so you will be safe to sell and make a profit.
If you sell it when the price is at $9,5k, you can sell it at that time but your profit will not too big.
If you are fine with that profit, then there is no worry if you want to sell in at that price.
But if the price drops at less than $8k, then I suggest you buy more bitcoin because the chance of bitcoin price to go back to $9k will wide open.
After you buy, you should be patient and don't panic until you can see the price can reach $9k again so you can sell your bitcoin which you already bought at less than $8k.