I just finished bottling my American IPA last weekend. It ended up sitting in the primary for 2 weeks & then 1 week of dry-hopping in my secondary.
At day 10 in the primary, I took a gravity reading & tasted the sample...same as yours, pretty bitter even though I only used 1 oz Simcoe for bittering at 60 minutes. At day 14 I took another reading. It was the same gravity so fermentation was complete, but it tasted 100% different/better than my first sample. The bitterness faded & my Chinook, Centennial, & Amarillo flavor hops really came through.
Your beer will mellow as it bottle conditions. You probably still had some hop particles in suspension when you tasted your sample. As your beer ages, everything will settle out at the bottom of the bottle & your flavor will come through as the bitterness fades.