Ok so you got a hit, sweep it with your searchcoil several times to make sure the target siginal doesn't disappear on you because it's below your discrimination setting, ie. small pocket of rust, or small trash target. If nothing else sidestep 90 degrees and see if your still getting a siginal. So you still have a siginal, now move your coil a few inches to either side of where you seen your coil pass when it beeped and tap your pinpoint button on the detector and in a slow move guide your coil to the target listening to the increase in pitch of the tone as you near the target.
I watch the depth meter closely also at this time. So you hear the tone get louder and the depth gets shallower. When the tone pitch just starts to decrease and depth readout increases by even 1/2 inch back the coil up a hair. Than either push or pull the coil to you or away again listening and watching the depth meter for any changes in tone or depth positive or negative. Personally I sidestep 90 degrees usually instead of the push pull method. I'm assuming your detector has the round concentric coil, so when your target sounds the loudest and reads the shallowest from those two directions 90 degrees apart from each other on your Whites that coin WILL BE right down below the inside of that center circle on your coil.
Don't totally rely on your target being at the depth your meter said it was. That can vary especially in a non coin target by it size and depth.
As others have said your target could actually be in the sidewall of your hole (sometimes). Also as others said a handheld pinpointer is a tremendous aid once your hole is dug and plug removed locating your actual dug object.
If your on a budget buy a Whites Bullseye pinpointer, if you can spend a little more get their TRX pinpointer, or a Garrett model or whatever. Harbor freight sells a cheap one,buts Thats just what they are too. I bought one in a pinch once but wouldn't give a nickel for another. Hope this helps and good luck and happy hunting. It's addictive!