I love the purple tones in this picture, first of all. I'm not especially big on frames, and IMO, the purple frame isn't really helping the image. And if it's not actively helping, get rid of it. Removing the brown in the lower corner and the caramel would also help the image, IMO. For me, what I love about this picture is the cool colors, and those two sets of warmer browns are detracting from the color composition of the image.
Just what would have helped me like it a little more. As it stands, I do like the image, and if I had voted on this challenge, I probably would have been one of the people raising your avg.
Strictly my opinion, take it for what its worth...The score on this image, I believe, is not due to the quality of the image, its due to its relation to the topic. You have a very pretty flower but not a wow flower, in a challenge full of wow flowers. If this were a challenge on cakes, I think this would have done a little better, as you captured the cake with good lighting (so many pictures of food here have bad lighting making the food look inedible!). To up your score a little more, you might have taken the shot at an angle more flattering to the cake (not cropped through the middle of the cake). The background works well as does the natural white lighting on the whole scene. Maybe try a square crop that includes the bottom of the cake with part of a plate in a complementary color. At any rate, remember that part of your score is always going to be relation to the challenge. Quality of the image itself only plays a part. You got some 10s, 9s, and 8s. Can't be all bad! :)
As said, 5.5 aint bad. I gave it a 6. It is very sharp and the color on the flower is great. Just not an overall "Wow" shot. Looks delicious though! Happy belated Birthday.
6 - Nice flower, and food shot - just looks like it is 'cut off' at the base/bottom, which the frame emphasizes. Perhaps a variation in the composition, with the flower more centered, or different angle, make this better in my opinion.