Hi, welcome ab
Your novorapid has one purpose in life, to quickly reduce the effects of what you eat or drink, so if your blood sugar rises beyond what you want it to be, after you have eaten, then you should inject the novo, the trick is working out how much and when, (20mins before food for me) finding out when is the right time for you, takes time and should not be rushed to avoid hypos. No one can tell you the answer as its different for everyone.
For me, eating sandwich and crisps would spike me badly because it’s very high in carbohydrates so I would absolutely need my Novo, I try to keep my carbs down and therefore my insulin down, stick around and have a read of the forum, lots of useful information here, good luck.