The reflections on the sides are of the exposed wood: you just need to correct that bit
. The bottom reflections are because you have the glass on a pane of glass as well as the white paper.
My product photography rig (which I should probably dig out of somewhere) was made with 2 pieces of rectangular (2:3) paper, placed like a T. The top sheet forms the base and rear panel, the lower sheet forms the sides. i have another one that has a section of where the sheets meet cut out of the top sheet to give me a bit more bend in the side sheets, but I rarely find that to be an issue.