Ask for a latte, it has no chocolate sprinkle. It's hardly the end of the world, I am sure I eat more than 10g of sugar from time to time. I just get back on the horse the next day. Depending on where you are, and on your own bodies responses, you might find that you crave sweet snacks for a few days, just resist it, or make something with dextrose if you need to, and you'll be fine.
You know, I don't think that our forefathers never ate more than 10 g of sugar in a day. I think it's just a convenient 'rule of thumb' in a world where it's easy to drown in sugar daily. I suspect they gained weight as they ate lots of fruit in season, and lost it through being fructose free through the other 9 months of the year. If you have the odd moment of eating more fruit than usual, or even more sugar in other forms, you're not really doing any different. The trick is, we need to make sure we avoid it as much as possible. You haven't failed because you went 2 g over the amount David suggests you eat in a day. It's up to you what you do if it results in cravings, and either way, it's a LOT less sugar than you were eating before you were sugar free, you've hardly 'fallen off the wagon'.