Have been in the same boat, got a NovoPen Echo now which tells me how many units I took and how long a go I took them. As for your dilemma, if it were me I would monitor BGs for the next couple of hours. If much higher than normal I would take the normal shot and continue to monitor every hour until the morning. Have fast acting carbs at the ready in case you have double dosed. Do you take your Lantus every 24 or 12 hours?