Vinh Nguyen

So i have been working with a professor for part of my undergraduate degree, but i am finding that his research is not within my interests. He is not my official advisor, but he has helped me a bit with a fellowship application for a project that i have no enthusiasm for. Before it progresses any further, i very much want to try to at least go for something i enjoy more. He has been very nice to me, and i absolutely hate that my spinelessness has caused me to not voice my concerns earlier, and i have thus wasted his time. What can i do? Any advice would begreatly appreciated.