Question for ARKit worldmap

Hi there, I'm a beginner of ARKit, recently I'm trying to use the worldmap. I set up everything and packaged it in my iPad then tested it in a shopping mall, but the location is not that accurate, the object I placed shows at a wrong place after I loaded the scene I saved. The margin of error was plus or minus 2 meters. I think it might be the shopping mall was too big which causes the error. Because I tried it at a storeroom which is much more smaller and everything works perfectly. So I just want ask if there is any solution for worldmap when using it in a big scene like a shopping mall with less error. Thanks in advance.