Hi,
firstly don't beat yourself up! a couple of slices of ham isn't a problem... if you're on day three then you have already done two full days of only 600kcal going in to your body! that is going to mean you're already a couple of thousand kcal down for this week!!!!
now day three... you have your 600kcal and then have some ham, lets say its proper fatty ham and made by the devil!!! and its 1000kcal (which it would need to be some evil stuff for that!!!) then today at worst case you are 1600kcal and worst case you are going to be balanced today, so you write that day off. are you at day one? no, you have done two solid days so your body is at least that 2000-3000 kcal down since you started. We all have blips.
BUT!!! you've had your blip now some come on lets crack on and lets get this first week seen out properly lass! The first week is the hardest so if you're going to have a blip now is when its going to happen but don't lose sight of that end result, when i'm feeling a bit low i go and try on some jeans that are tight or a top that makes me look like a jelly belly to remind myself where i am and where i don't want to be.
Come back here tonight and tell us that you've had a 100% day!!!