Did I blow my chance with him?

I recently told a guy that I liked him a lot and when he asked me why, I couldn’t come up with a response. I was flustered and didn’t know what to say. He just laughed and told me it was probably an infatuation. The thing is, I know I am madly in love with him but because I didn’t say anything at the time, he has dismissed me already and may not take me or my feelings seriously. It feels as if I had a chance and blew it. How do I fix this and convince him that what I feel is real even if I am not good at explaining things? I don’t want to lose him, and I want him to believe me.
Not being able to articulate how you feel is normal and you shouldn’t feel awful about it. If you can’t explain this, try writing down why you think he matters to you. If that is difficult too, try other cues that show him you care. Letting him know that you are aware of how he is, or what is important to him, may convey your message through actions rather than words. If he doesn’t take you seriously, it’s also possible that he just doesn’t reciprocate your feelings, which is why it is important not to be too hard on yourself and assume that this isn’t working just because you can’t respond to a question. Give him time, let him think about what you have said, and he may change his mind about how he sees you.

Should I even try to make a long-distance relationship work? I know it’s going to be challenging and don’t know if I am up to putting in all this effort.
It is a lot of effort, and it cannot be done without both partners committing to make it work. If you have doubts about it, speak to your partner. If that doesn’t help, and one of you isn’t ready, the chances of it lasting are slim.