need help letting someone down easy

Okay so this guy saw me sitting by myself and asked for my number. And I panicked and gave it to him even though I'm uninterested. He's 26 and I'm 20 and I think that's a huge age gap and I kind of want to use that as my excuse. I literally met him today and he text me like 5 seconds after I gave him my number. He gives me a really creepy vibe but I wanna let him down easily. Is this an okay response or how else should I say it?