I’ve just seen that you’re very recently diagnosed
@FieldD88 I’m guessing you’re on fixed amounts of Novorapid and haven’t been shown how to count carbs and adjust your mealtime insulin yet. In that case, you can either think of similar meals you’ve eaten and what your blood sugar was afterwards (ie how did your 5 units work for you) and then, depending on that answer, eat a certain proportion of your lunch carbs; or you can eat the whole lunch but be prepared to be high. I’d go for the first option in your situation. I’d also test extra to see how things are going.
It’s good to get into a routine of checking your diabetic stuff before you go out. It’s so easy to grab stuff and assume it’s ok. I made exactly the same mistake as you with my pen many years ago - grabbed it off the kitchen top but only realised it was almost empty when I got to my lunch venue. I’ve also tapped my bag to make sure I could feel the glucose tablets - only to find it wasn’t a full packet of Dextro, it was an asthma inhaler! So, it’s easily done. Now I always take a few extra seconds to look at everything: visually verify my glucose, look in my pen case to check it has insulin and spare needles, check I still have snacks in my bag rather than assuming, etc etc.
I hope you still enjoy your lunch.