If you are going to use a uv mapped object to apply a image/color on Full Colored Sandstone, it has to be in VMRL format. Oddly when you upload the model, SW recognizes each basic unit length as 1 meter!! So if your model is 10 x 10 x 10, the printer will try to print a model 10m x 10m x 10m. Which it can't do, so it gets scaled to a size that will print, so wrong dimensions.
Post a ink to the file, its easier to diagnose a problem.
Use Meshlab to convert your file to VMRL .If the UV mapping is looks ok in Meshlab, it will export to SW if the model has a proper mesh.
In Meshlab if you want to see the bounding box dimensions use this Filters/Quality measure and computations/compute geographic measurements
If you want to scale the object use this, Filters/Normals/Curvature/Orientation>Transform scale. A slight problem can occur with uploading . Scroll down on the link provided below to see what changes are needed. Makes sense actually since only access to the UV texture is in the zipped file you upload.
https://www.shapeways.com/tutorials/textured_models_with_sket chup_and_meshlab
The .x3D format after tests proved to be a better format to export with if you have several different materials plus a uv texture on your model. The wrl only seems to support 1 material and a texture. With .x3D much more options for a colored model