Star the 3.4 is what has thrown you out. 3.4 is actually too low, it is called a hypo to most diabetics. What your body has done has respond to that by releasing glucose stores from your body to correct it so that plus your sandwich has made your blood sugars a bit higher. I wouldnt worry about that one result, it ill likely not happen again. Also you can put the margarine or butter back on the sandwich if you like because the fat in it actually helps to slow down digestion and even out the blood sugar curve. The sandwich you had sounds really healthy and it is but it is also going to be absorbed quite quickly as there is not fat content to even out the digestion process. Does that make sense?