You may have to remove the Mendeley field code from your document before handing it in. All citations that you have added are linked to the references in your Mendeley library. If someone opens your document without having access to your library this connection will not work and the references may not look as they should. The easiest way of removing the field code is to export the document as a PDF file. You do this under File > Export > Create PDF-/XPS. This will create a PDF copy of your document where the citations and bibliography look as they should. If you want to keep working on your text you can do so in the original document where the field code is still intact.