How to say no

I went on a date with a guy and I did not have the best time. I was content with moving on with my life after the date. The whole time I felt just uncomfortable. He caught me on a walk home from class and asked me out again. I do NOT want to go but I panicked and didnt really say anything other than “we’ll talk about it after thanksgiving” so now idk what to say?? I know the best approach is to be honest and say no thanks but I feel bad. Any tips on how to make it easier?