GUI: waiting for a checkbox to be checked to carry on in a callback function

I am trying to write a GUI in which I visualise some figures and I then have to make an action when and only when the user has made a choice. But my program doesn't seem to respect the order, that means it goes on and back to the beginning without waiting for the answer. Here is a simplified version of my function called in a gui:

    function ExFctCallback(src,evt)
      set([S.FigInt,S.ExFct],'Visible','Off');
      % Get workspace variables
      fig = get(S.FigInt,'Value');
      I = S.imx;
      imshow(I)
      pause(2)
      I = im2bw(I);
      imshow(I)
      pause(2)

% Call a function that gives kp as an output  
    if ~masde2
      keeperIndexes = kp(1:2);
    else
      couleurs = ['r','g','c','m','y','b'];
      lkp = length(kp);
      couleurs = couleurs(1:lkp);
      set([S.CircCh,S.ChooseCirc(1:lkp), S.ChosenCirc],'Visible','on');
      if (get(S.ChosenCirc,'Value')==1)
        valcol = get(S.ChooseCirc,'val'); % Keep chosen values in a cell
        valcol = logical(cell2mat(valcol));  % Transform the cell 2 matrix of logical
        if (sum(valcol) ~=2)
          set(S.ChosenCirc,'Value',0);
        else
          keeperIndexes = kp(valcol);
        end
      end
    end
    % I just want to carry on when keeperIndexes has been initialised
    if exist('keeperIndexes','var')
      [estDist,S.dist] = fct2(...);
    end

      % At the end of the procedure, the execution buttons disappear and
      % only the one to load a new fig stays visible.
      set([S.CircCh,S.ChooseCirc, S.ChosenCirc],'Visible','Off');

    end % ExFctCallback

Now the buttons of interest are the following ones:

% Choice of the colours of the circle
inleft = 150; sepleft = 25;
couleurs = {'red';'green';'cyan';'magenta';'yellow';'blue'};
Tipstr = 'Select the 2 colours corresponding to the correct diameter of the circles';
S.CircCh  = uicontrol(S.f,'Style','text','Units','characters',...
        'Position',[170 28 38 4],...
        'String','Choose the 2 correct circles',...
        'TooltipString',Tipstr,...
        'Parent',S.botPanel,...
        'Visible','Off',...
        'FontSize',12);     
for k = 1:length(couleurs)
  S.ChooseCirc(k) = uicontrol(S.f,'Style','rad','Units','characters',...
    'Position',[inleft+sepleft*(k-1) 27 18 2],...
    'String',couleurs{k},...
    'BackgroundColor',couleurs{k},...
    'Parent',S.botPanel,...
    'FontSize',12,...
    'Visible','Off');
end
S.ChosenCirc  = uicontrol(S.f,'Style','check','Units','characters',...
        'Position',[190 24 8 4],...
        'String','Done',...
        'min',0,'max',1,...
        'Parent',S.botPanel,...
        'Value',0,...
        'Visible','Off');

So what I want is first to visualise the original image, then the B&W one and then nothing happens until the user has selected exactly two colours (from the ChooseCirc radiobuttons) and confirmed it with the check button ChosenCirc. But what happens is while the user decides, the original and b&w pictures appear again and again without waiting for the procedure to carry on.

I know it is a bit messy but I have tried to explain it the best I could ;-) I can include some screenshots if it helps. Cheers.

[Adam]

What is ExFctCallback responding to? Should it only execute once?

If the user is expected to confirm something and then trigger a calculation would you not be better with a pushbutton than a checkbox? What you report suggests that your ExFctCallback keeps triggering before it is ready which suggests it is reacting to the wrong trigger.