Oops. You sent a message that you wish you didn't have. Can you cancel sending a DM on Instagram? Fortunately, you can, although it doesn't help if the recipient has seen it before.
Long press the message you want to remove. Two options will appear: Copy and Do not send . The latter will make it disappear entirely from the thread.
Instagram often tells you if the other person also read the post. It will say "Seen" below the message. However, if the other person's notifications are turned on, they'll likely have seen it already.