This usually means the focusing screen is not positioned at exactly the right height. Autofocus can still be correct because it uses a separate AF sensor, but manual focus through the viewfinder depends on the focusing screen being precisely aligned with the camera’s image plane.

Many focusing screens use thin shims to set that position. If the screen sits slightly too high or too low, what looks sharp in the viewfinder won’t match what the sensor records. So the fix is typically to calibrate the screen position by adjusting or adding/removing the small rectangular shims used with the screen.

If your replacement screen came with shims, those are likely intended for this adjustment. If not, check whether the original screen had any. In short: you probably didn’t damage anything, but the screen likely needs shim calibration rather than just basic installation.