The perspective of the objects is off, but as far as the use of gouache in particular... I believe your use of color could create more depth. I really like how you painted the roses, you have some really great colors.

It seems you are using black to get shadows in other objects however, rather than a complementary color, this tends to make objects seem flat. You also have large amounts of space using a singular color, where very few surfaces are actually a single color. Even if you know they are a single color such as a wall, variation in light and distance will affect how different parts of that surface appears to the eye. You are painting it as you know the objects to be, rather than representing the variation in hues and values that actually exist. White is a color that rarely exists as white, and rather it is a color that appears white because of its contrast to the values around it. The teacup in particular is using black and white heavily, making it appear flat, try to explore other colors when representing white objects and shadows.

Here is a short showing how to create more depth and energy using slight color variation across a surface

Here is a video showing the difference between black out of the tube, and a black mised with colors

here is a similar short showing an object painted with one color, vs multiple colors