Hi Davey,
Try not to over think LL. It really is as simple as eat the 4 packs spread over the day, and drink the 3 to 4 litres of water, and black leaf tea or coffee. Try not to worry about ketosis and the exact moment it starts. Stick to it and it just works, don't worry about it. Keep your mind busy with other things, read some diaries of successful LL'ers who have reached goal. They are really inspiring.
You will have already cut down your calories so much in just 3 days, get back to LL until Tuesday weighin and you WILL still see results for your first week. Get over this one blip, don't throw away your hard work. In the meetings you'll learn about all or nothing thinking, and that you need to change that thinking, instead make the decision to stick to this. Every time your tempted make the decision again.
From experience I'd recommend to Keep away from food, don't go near it for the first week. Don't open the fridge or cupboards that have food in. Dont' talk about it, smell it, or even think about it. In a couple of weeks when it gets easier it won't even bother you to sit with others who are eating. You will be so happy with your losses that you won't want to break it.
We are all here to support you...