This doesn't look like too much to me. How long do your meals keep you satisfied? You're aiming for 4-5 hours between meals. If you're hungry before four hours, they're a bit small. If you're regularly going 6-8 hours without feeling hungry, they may be a little too big.
It's not unusual for people to feel that they're eating too much on a Whole30. Part of this is that when you take away carbs like bread and pasta and replace them mostly with vegetables, it can take a lot of vegetables to get the same feeling of fullness you would experience with those foods, so the volume of food may truly be bigger than you're used to. Another part of it, at least for some people, is that they're used to diets that restrict calories, which Whole30 doesn't do, so if you've come from that kind of background and now instead of counting calories you're starting to eat based on hunger and on fueling your body adequately, it's even more likely for your brain to now think a full plate of food is too much.