My lips didn't swell at all after the injection. Will they get even smaller?

Lack of swelling doesn't mean you won't get good results. It can take 1-2 weeks for final results. I would wait a full 2 weeks before judging the results. If it is after the two week wait, you can have the filler reversed with hyaluronidase.
I hope this helps!

Since you’ve had previous experiences with JUVÉDERM® in the past, I can see why you might be curious as to why you’re not seeing any swelling this time around. However, it is possible to react differently with each injection, especially if a slightly different product was used. But this doesn’t mean that your lips will get smaller. In fact, you should begin to see the volumizing effect you’re looking for over the next several days. If not, talk to your injector about the possibility of adding more. For now, sit tight and give the product 10 days or so to start producing results.

There are different properties of different fillers. There is a difference between Juvederm 2 and 4. Juvederm 4 is much more viscous and binds less water than Juvederm 2. It also lasts longer. That explains your experience with swelling. The most important is to have your lips looking natural as a integral part of your face and not as a separate feature. Good luck!