Based on what you've said here's how I would class your day's eats!
porridge - healthy extra B for 28g
mullerlight - free!
alpen bar - alpen light is 3 syns each or 2 for a healthy extra B. As you've had a B choice already you would have to syn it. Normal alpen bars are roughly 6 syns each (they don't count as a healthy extra)
fruit - free!
mushroom and pasta dish - free!
Creme fraiche - 3 syns for a tablespoon of full fat creme fraiche, 1.5 syns of reduced fat.
So based on what you've eaten you only have to syn the alpen bar and creme fraiche.
I think the general consensus is that you don't literally have to have it on your plate. I think the reason they state 1/3 on your plate is for portion control so you don't go overboard with the meat/carbs. For the majority of people who struggle with portion size this is a sensible precauition to take. However, as long as you are either having your superfree as a starter, hence already partially filling your stomach before the meat/carbs or, being careful to have a smaller plate of meat/carbs to leave a third of your dinner allowance for fruit afterwards you should be ok. It's all about using some common sense, failing that i'd just leave room on my plate and stick the bloody melon on it and eat it last
I know sometimes people get accused of "tweaking" but for goodness sakes we can apply some common sense!