Kaylz! Don't worry! 8.4 is still a safe level to be at, even though it wasn't quite what you were looking for, long term, just before lunch.
Several things could be going on here, and you can't tell much from a one off experiment. Maybe your body treats porridge as a particularly slow release form of carb, so you need to bolus a bit later. Maybe your bolus was all used up after three hours, and your basal wasn't quite covering the gap. Who knows?
I couldn't possibly work out which was causing the late rise, until I'd eaten porridge for several days, recorded the results, and looked for a pattern emerging.
As to not daring to eat because you're in the 8s - this is what a correction dose is for, just let your meter work out what you need, and it will take into account what your starting level is.