It’s your own new car. You paid for it, you decide what you like to do with it. No apology needed. You like the new car smell? I can see that. New cars, the passenger compartments, they do have a pleasing aroma. I can understand you want to preserve that as long as possible.
I’m not myself so concerned with the smell. But I do understand what you are saying. When I purchased my first car as a teenager I used to tune it up every weekend. I’d check all the fluid levels, top them off even if they were a few ounces low, then check the dwell, the timing, the idle rpm, and tweak the carb mixture screws until it purred like a kitten. Then the next weekend, I’d do it all again! It was pretty fun. I should say I no longer am quite as diligent. Actually I’m nowhere as diligent. But that was then, this is now.
hmmm … so back to your question … hmm m… well, there’s not much you can do to keep the existing new car aroma inside indefinitely. Even with the windows up, the HVAC is usually circulating outside air in, and inside air out. How much depends on how you set up the controls. And air leaks out all the time anyway. Take a look at the door threshold area. Those are usually designed to have non-sealed openings between the door and the threshold so air can exit the passenger compartment, but not allow rain in. Often there’s something like that in the rear side window trim too. It’s part of the fresh air ventilation design. For outside air to get in, inside air has to have a way to get out.
So eventually that new car smell will go away. But there’s products sold in auto parts stores for this very purpose. That’s the first place to check. I think you can get a pretty good result just by keeping the inside well vacuumed, all the hard surfaces wiped clean once a week, and using Windex on the inside of all the windows as often as practical. Windex sort of has that new car aroma all by itself.