Hi Stocksplacement,
The window for 'Netwise/Daywise' position, aslo has a Square off button. Once you choose the actual position that you are in, you should be able to square it off (although I have not used this button till now.. will use it on monday and keep you updated).
Alternatively, Once you have bought a lot(in case of FnO), when you try to sell it, it first tries to square off the position; rather than creating another position.
(My personal experience... I have tried the alternate route.. and it works.)
Regards
ARsh