A quick platform question

If I am long 10 EURUSD at 1.3567 with a stop at 1.3500 and I want to reverse and go short at that point should my SELL TO CLOSE be for 20?

I noticed I could not put in a SELL TO CLOSE for 10 and a seperate SELL TO OPEN for 10 as the system would not allow the entry.

Please explain how to do this on this trading platform. Thanks in advance.