Timing a Bolus

what if you have bolused for eating, and midway through your meal, you decide you want more food (carbs) than you originally bloused for. do you take a second bolus and continue eating, or do you wait another 15 to 20 minutes before eating the extra food?

if my BGs are in a good range/on the lower side, i can’t wait any more than 15 minutes for pre-bolusing and eating my meal. otherwise, i start to go low very quickly. and this is regardless of whether i am eating a high or a low carb meal. i usually eat mostly protein, though, so maybe that makes a difference w/ regard to when i need to bolus. but i think it would be the opposite: carbs digest quickly, while protein digests a little more slowly. ???