If you're aware of your mistakes, then you should probably slow down when answering the questions to make sure you've done it correctly.
I haven't had to do this myself, but maybe it would help if you used a hand gesture as an aid? If you need to plot (a,b) then first look at the value 'a' and drag your finger (pointed vertically on the page) from left to right across the plane until your finger is covering the required x-value of a. Your finger will be in the position of the line x=a. You can lightly trace a short portion of the line x=a too so that you don't need to hold your finger there any longer.
Once you have that line traced, just plot the y-value of b on that line and you've found your coordinate.
So remember: finger pointed vertically that you drag left to map the x coordinate.