Hi Iris, I was wandering around the Discover page and saw your design had the dreaded streaked floor problem. To fix that, click on the floor, then in the left panel click the Delete Floor button. You should now see a different floor underneath. Use the Delete Floor button again. Once you are down to the white grid, then delete one wall, then redraw it (normally, any wall will work, so use one that doesn't have windows/items on it).
You should see the floor restore to the default texture. Then just drag and drop textures from the left hand panel or your 'Room materials' tab.
Here's an old thread that explains the construction problem that causes it: https://roomstyler.com/forum/discussions/6395