Hi katsmad64. I know exactly how you feel, I've been there more times than I can even begin to remember! First of all, don't beat yourself up over it, we all have slips and days where we eat everything we shouldn't. You've already realised that you've strayed off plan and it was only one day so it's easily fixed, just stick to plan for the rest of the week and I'm sure you'll soon get back on track.
I know what you mean about it messing with your head and being complicated. In the past I've tried every diet I could think of - SW, WW, low cal, meal replacement with shakes, Harcombe, low fat, low carb and they all tell us completely different things! I find that switching diets gets confusing because you spend X amount of time convincing yourself that the diet you're on is the right way to eat, then you get to a point where you can't stick to it any more, switch diets and then have to convince yourself that what you're doing this time is the right thing. After a while everything seems to contradict itself and you don't know where you are. The best thing to do if you want to follow SW is to forget everything you've taught yourself before and to fully focus and follow the SW plan. It does work, we've all seen the proof, as long as you stick with it.
I still have days when I stray and think about making up my own rules so that they fit in with my diet because 'that's what I did once in the past and I lost 3lbs doing that' but in the end it just comes back to bite me in the @$$. Just try not to beat yourself up on the slips, draw a line under them and get back on plan as soon as you can.
Try to stay off those scales too, your weight will fluctuate on a daily basis regardless of what you eat, it's only natural, so weighing once a week should be the minimum amount of time you leave between weigh-ins, if only for your own peace of mind.
Good luck, I know you can do it!