Help with subtraction in a "while" loop

I am coding a section of a task using psychophysics toolbox in which I am trying to use two keys on a button box to increase or decrease a participant's mood rating and a third key to finalize an answer. I am running into a problem in which once a key is selected (say, the third key, which corresponds to resp = 3) the subtraction just continues until another key is selected. I want to code it such that the program waits for a key response, increases/decreases/or finalizes the rating ONCE and then waits for an additional key response. I'm not sure where my code is going wrong, keep in mind that I've very novice in this area!

while GetSecs - starttiming <= trialtime; 
    resp = 0;
    [h,w,~] = size(IMAGE);
    aspectRatio = w/h;
    height = 800;
    width = height .* aspectRatio;
    imageRect = [0 0 width, height];
    centRect = CenterRectOnPointd(imageRect,screenXpixels * 0.5, screenYpixels * 0.5);

    Screen('DrawTexture', expWin, currIMAGEtxr,[], centRect); % draws self assessment manikan to screen at centRect location
    Screen('FrameRect', expWin, 0, centRect, 5);
    DrawFormattedText(expWin, sprintf('Use the green and blue keys to change your valence rating.\n\nPress yellow to enter your selection.\n\n'),'center',100);
    DrawFormattedText(expWin, sprintf('Your rating is %d.\n\n',rating_val),'center',950);
    Screen('Flip', expWin);
    if ~isempty(inputaddress)
        [resp,datum] = SAM_resp_final(tp.buttonpolltime{1},inputaddress,...
        outputaddress,trialtime,flipinterval); %collect participant's response

        WaitSecs(.002); %wait 2ms as flnkrresp script writes to the parallel port
    end
        outp(outputaddress,0); %reset byte
    
    if resp == 3;
            rating_val = rating_val + 1;
            continue
    elseif resp == 4;
            rating_val = rating_val - 1;
            continue
    elseif resp == 2;
            Screen('DrawTexture', expWin, currIMAGEtxr,[], centRect); % draws IAPS to screen at centRect location
            Screen('FrameRect', expWin, 0, centRect, 5);
            DrawFormattedText(expWin, sprintf('Press the yellow key to confirm\n\nPress green or blue to change.'),'center',100);
            DrawFormattedText(expWin, sprintf('Your rating is %d.\n\n',rating_val),'center',950);
            Screen('Flip', expWin);
                if resp == 3;
                    rating_val = rating_val + 1;
                    continue
                elseif resp == 4;
                    rating_val = rating_val - 1;
                    continue
                elseif resp == 2;

                        Screen('Flip', expWin); 
                        return
                end
     elseif resp == 1;
            Screen('DrawTexture', expWin, currIMAGEtxr,[], centRect); % draws SAM to screen at centRect location
            Screen('FrameRect', expWin, 0, centRect, 5);
            DrawFormattedText(expWin, sprintf('Incorrect key press!\n\nPress the yellow key to confirm.\n\nPress green or blue to change.'),'center',100);
            DrawFormattedText(expWin, sprintf('Your rating is %d.\n\n',rating_val),'center',950);
            Screen('Flip', expWin);
            continue
    elseif resp == 0;
        continue
     end
end