It sounds like you are doing well so far! Thank you for your commitment.
I find the key to 'hitting the ground running' is master the skill that you'll be taught/using in the retreat as soon as possible. Meaning; meditate as much as you can everyday (3-4+ hours), stay as mindful as you can throughout your day and stay confident in your ability to get SE.
Something I found that helped was 'desensitizing' myself to 'pleasures'. What I mean by that is help your mind lower it's craving by not eating foods you REALLY want to eat, just eat to get the nutrition. Don't move out of a little discomfort. Try to stop fidgeting, try not listen to music/wearing cologne/perfume or deoderant. Essentially try to live a 'boring' life while on this practice. This helped me crave less because I wasn't indulging as much.
Good luck

you can do it.