Couple of choices, like less hops, or less boiling, or (as you asked) different hops. 5 ounces is a bit much - I've used more, but for special reasons.
Bitterness comes from the time the hops are exposed to high temperatures (essentially, the boil). Either use less hops, or boil them less time, or both.
Time: 30 vs. 60 minutes won't change it a lot, but it'll be about half at 15 minutes and about a quarter at 5 minutes.
Quantity: an ounce is a decent amount. Maybe an ounce at the start, and another ounce when you stop the heat. That'll give you bitterness and flavor, but not as powerful.
Different: bitterness is bitterness, and most hops are just as bitter as another, so no sense in changing. But Centennial also has flavor, a bit grapefruity, while other hops have different flavors. What flavor(s) are you looking for?
Finally: Brewers Friend has a recipe builder. If you enter your ingredients accurately, it can help you predict how it will turn out. It works pretty well, but if you have questions about what it tells you, just ask. For example, a beer with 15 IBU of bitterness is not very bitter, maybe like Budweiser, while a beer with 50 IBU is pretty bitter, maybe more than Sierra Nevada pale ale.
Oh, and welcome!
