Press D to reset your colours again, just in case. Press G to select your Gradient Tool again and then click on your Gradient in the Options bar. In the Gradient Editor dialog box, select the Foreground to Background preset.
With your Drop Shadow layer’s Layer Mask selected, drag your gradient from top left to lower right, over the lower part of your shadow. You don’t want your shadow to disappear completely, just soften the edge a bit.
You can now adjust your individual Layer Style layers to fine-tune the effect. Once you’ve tuned the styles, you’ll want to select your Highlight layer, hold the Shift key, and then select the bottom-most Style layer, Drop Shadow. Press Ctrl + E to merge all of the layers.