Hi Josclyn,
Snapping to grid can sometimes depend on the percentage of zoom you are in snapping your object. For example, at 16.5%,%, snapping can be a very inaccurate, you would know if you zoomed in and steam over how much space there is between the object and grid. I would suggest that you zoom in quite close to try and accomplish it. For detailed work, you can also try nudging the object with your arrow keys on the keyboard (This also depends on the zoom percentage as there is a direct correlation between that and the increment of pixels traveled.) . If the above wasn't the case and you believe that photoshop is malfunctioning, hold down the CTRL key while dragging and then compare the snapping result to without the CTRL. Pressing CTRL while dragging should exempt the item from snapping to anything and hopefully there is a difference between the two.
As a last resort, you may want to use guides. |