Hard to know what went on. He could have dropped low and bounced or it could be 2 units wasn't enough.
I know you can really go though strips, but the more tests, the easier the puzzle of Larry is to figure out. These early days are all about gathering data, see what this dose does at this number, does this dose make it better or worse?
You are also dealing with N, which is a short acting insulin, so we can't be sure whether it is wearing out before the next preshot or whether the dose is too low.
The only sure thing I see is that 3 units was too high a dose because you got a yellow at +12, 4 hours after the N would normally wear off. Long cycles often mean a dose that is too high. So I wouldn't go back up to 3 units.
The more information (numbers) you can give us, the better advice we can give you. But we realize it's hard in the beginning - you're just learning how, Larry's ears haven't toughened up. So both of us have to be patient, and we will give you the best advice we can in the meantime.