Praise be to Allaah.
If a man has seen enough of his fiancée, within the limits set by Islam, to enable him to decide whether to go ahead with the marriage or not, then it is not permissible for her to uncover any part of her body in front of him until after the nikaah. (See also question #2246 and #2572). And Allaah knows best.
Sheikh Muhammed Salih Al-Munajjid