I'm a bit confused... Were the jelly babies supposed to be your sugar load? In that case I think it might be best to mention it. They might just keep you there for an extra hour to do the test right. Otherwise, it might not be accurate and you could end up second-guessing the results no matter if it's positive or negative.
That said, it sounds a bit strange. Usually you need to fast for 8-10 hours beforehand and then they need a fasting blood draw as well as the ones after the sugar load. There are 2 different protocols, both valid. The 2-step one involves a simple screening done first, where they give 50 gr of glucose and get fasting and 1-hour levels. If you fail that, they make you take the 3-hour test, where they give you 100 gr of glucose and get fasting and 1-hour, 2-hour and 3-hour levels. The 3-hour test makes the final diagnosis. The alternative 1-step method is to give 75 gr of glucose and get fasting and 1-hour and 2-hour levels. I can't decide which one they're having you do kelz86, because they all require fasting levels as well. Although some practices do go for some simplified methods other than the ones usually recommended... In any case, mixing up the post-glucose times or having eaten before the fasting levels can mix up your test results. So, yeah, long story short, it would probably be best to let them know.