eating smaller meals

In Italy you can order and eat whatever you want. If you just want a salad or a side dish it’s ok. Nobody will say anything. Unlike France.

The menu has separate sections for Antipasti (salads, small plates of meat or cheese, etc.) , Primi (pasta, gnocchi, risotto), and Secondi ( meat and fish dishes). Sometimes there is a pizza section as well. You can order o single dish from any group and say that is all you want.

You can definitely order 'primi piatti' for your meal. I did and it was plenty of food for me.

Your money, so order exactly what you want.
In Italy, I’ve only ever eaten one course in a restaurant.
Then you walk to digest your dinner, and have gelato as you go!

or will this be interpreted as antipasti

A starter remains a starter even if you eat it for breakfast, but assuming the waiter interpreted it as an "antipasti"... What Would it matter to you anyways? What are you actually worried about?

Nobody's forcing you to order another "Primi Piatti" because a starter is somehow mandatory. Just like all the other dishes on the menu, eat what you want in any order you want. You'll be served by waiters, not grannies whose first & main question is always: "did you eat enough?"

I usually have a appetizer if I eat out here in Canada and do the same in Europe…never an issue anywhere I’ve been.

No issues at all. Usually I just have a pasta dish, occasionally just a salad. And during my last trip to several smaller cities, I had a few evenings in some of the small piazzas where I just had the Aperol spritz with some accompanying finger food and that was plenty for my dinner since I had a late afternoon gelato.

Everything is a la carte, so eat what you please. This is one of the things I love about Italy.

The only food item you are compelled to eat, every time it is available, is gelato!