It's your browser. Try opening the image in the PJ Image Specs tool, perhaps? I think that does its own scaling, independent of the browser.

Yeah, the corners are the darkest, since they're where the padding is thinnest, that's where it's attached to the wall. Elsewhere, it puffs out, these puffed out bits get the light and block it from reaching the attachment points. The shape of the puffy part, therefore, is a square with rounded corners rather than the hard square you've been drawing. Think less "tiles", more upholstery.

Some of the bricks on the oven look too detailed. Try to avoid giving brick a shadow and a highlight, as it creates an overwhelming about of detail. In particular, bricks in shadow should generally be fairly flat (no highlights), since there's less light hitting them. You could also reduce the contrast on all the bricks a little, e.g. by eliminating the brightest highlight colour.
The same is true of the tiled roof, it feels too detailed. Keep things simple, add detail only where it's important to avoid distracting the player.

I like that you added some detail to the silhouette of the bricks, but I don't think you went far enough. Those single-pixel dips between the bricks can look like noise, especially when butting up against other objects. Try to have 1-3 pixel gaps, and maybe even have some spots where the gaps are deeper than a pixel, or have some bricks be thinner and not reach all the way to the edge.

The bricks on the slanting, shadowed part of the oven should probably be slanting rather than horizontal.

Will the roof and the oven always be together? If so, it would be a nice touch to have the roof cast a shadow on the oven. The slanting surface would make for an interesting shadow, and it would make the scene feel more cohesive.

The highlights on the barrels feel a bit flat since they have horizontal tops and don't "wrap" around with the perspective.

Lastly, watch for tangents. If you have every prop reach the edge of its tile, you'll have a lot of objects line up, which can hurt the readability of the scene and just looks very artificial. Have some of the smaller props not reach the edge, so that they're always a pixel or two from nearby props. Maybe have some of the props be rotated rather than perfectly aligned to the tile grid, to make the location feel more organic.

The pepper feels a little dull, I think you could push the hue-shifting more, e.g. by making the highlights warmer/orange-er.

Some of the sel-out looks a little weird to me, it just reads like a broken outline rather than a pepper. Since there's the flame background anyway, why not do external AA with it and leave the outline stay solid and consistent?

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I like the colours and poses! Are you planning to make blacklight version of them later?

The lighting/shading on their legs doesn't feel cohesive to me. The third one feels fine (the shadows are cast by her torso and arm), but the rest seem to have highlights in random places.

The second one's face (or rather, face-mask) feels a little side. The shape of it is fine, I think it could just use a larger shadow on one side to show it wrapping around the face.

The second one's abdomen has some dark shadows on it, what is creating those? On the other hand, the third one is leaning forward, but her belly's fully lit, when it should probably be in shadow.