Okay so a gain of 8lb isn't good but the only thing worse would the 8lb plus all the rest that you will put on if you don't climb back on the wagon. Be honest with yourself, you know it will happen!
But really I think it's nigh on impossible to put on 8lb of fat in one week. You may find that it's just water retention and will come off again as you settle back into the plan. You had a week of holiday, presumably off plan, and I hope a great time. So don't beat yourself up. You're entitled to have a good time on holiday! SW is for life and not a straitjacket that you can never take off.
Oh and by the way exercise is great so don't even think of cutting back. It's good for you in some many ways including weight loss, toning and improving your mood. Women generally don't have the hormonal make-up to build significant amounts of muscle to the extent that it could affect losses. And anyway muscle is good for weight loss because 1lb of muscle burns more calories than 1lb of fat, not only when you are exercising but over the course of the day and your other activities - even just watching the telly!