So, unless you ate about "6000 calories", its unlikely you actually gained much!! Especially if it was only today.... Since you have a range of calories in Spark, simply eat at the lower end for 2 or 3 days, and by the time of your next weekly weigh in, you probably won't notice the after effects of Birthday cake much. (For me its not Carb calories , but salt, that has the weight gain effect!!)
I do hope you had a great birthday, and wish you many healthy ones in your future!!