Keep it up, you are doing awesome!
Okay, I see Logan is up to 72 at around 4 hours after shot. You're going to want to stay up with him until at least +6 to +7 after the shot. ProZinc is a nice longer lasting insulin, but that means it's still working to drop that BGL. It's the food you are feeding that's keeping Logan out of danger.
Once he starts heading back up over 100, and you are past the +6 or seven mark, hopefully he'll be out of danger. What you are looking for is two tests that are going up without the aid of food or karo. That will show that the insulin is wearing off and he's out of danger.
Unfortunately, vets tend to increase dose in too big of increments. No human would suddenly double their insulin dose, and neither should Logan. Thank goodness you are home testing! 2 units is obviously too much for Logan. If AMPS is high enough, I suggest you give no more than 1.25 units.
In the future, if your pre-shot test is low, you can either:
Stall without feeding for 20 minutes and see if the BGL goes high enough.
Give a half dose if the pre-shot test seems high enough.
Give a token dose (25% of usual dose.)
Give a drop dose (literally barely any in the syringe)
Or skip insulin.
A day of high numbers is always safer than a dangerous low.
Oh, and when you are telling us times, give it to us in an hours plus format. He was __ at +4 means it was 4 hours after the shot, for example. The timing helps us help you, but telling us the time on the clock doesn't help us much, as we are all in different time zones.