How to make this gradient drop shadow?

I imagine one of the reasons why you are having difficulty with this shadow is because it kind of gets smaller in the center, it doesn’t go all the way to the ends.

I would re-create it using a new element:

• Create a white rectangle (your page) over a gray background

• In a nee layer under the rectangle, draw a black oval shape the size of your desired shadow

• Select the oval, go to Filter > Blur > Gaussian Blur and blur your shape until it looks like the shadow. Because it’s under the white rectangle, you should only see the bottom part.

You can also add a little drop-shadow to the white paper, minimal.