Please help with encounter map (Gimp)

[Dolmen Creative]

Hi everyone!

I am trying my hand at a battle map/encounter map and I've put together a sample using Gimp along with all of the sample's attributes and my ultimate goal. Please feel free to comment, critique, laugh at, and lend suggestions.

Layer 1: "Wall Layer" (top) - 17pxl diameter paintbrush, black
Layer 2: "Wall Background Layer" - Filled whole canvas with white and trimmed out the corridor area using the Fuzzy Select Tool (based on layer 1)
Layer 3: "Drop Shadow Layuer" - Offset (X=0, Y=0), 23pxl, 80% opacity
Layer 4: "Grid Layer" - 100 x 100 pixel grid, 1pxl wide lines, black
Layer 5: "Floor Texture" - Filled whole canvas with "Paper" pattern fill, Van Gogh (LIC) artistic filter (gradient, with source image, brightness, effect image=layer 5, filter length=5.0, noise magnitude=2.0, integration steps=25.0, minimum value=-25.0, maximum value=25.0)
Layer 6: "Background" (bottom) - Whole layer is just a transparent base

I see areas I dislike on this (namely some white spots showing up around the wall layer) and I would like the floor to look like stone tiles (like the Skeleton Key Games tiles) and be a lighter base color of grey. Can anyone help me out with this? Thanks.