<human>: Summarize the given text in a few sentences.

I work in retail (nothing fancy, just a chain store).
Today one of my regular customers comes in and we start chatting about movies and TV shows like we normally do. A few minutes later, after looking helping him/her find some things, he/she asks if I would like to get together and watch a movie that we were talking about, without thinking about it I said yes and wrote down my number. 
I only did that because I really didn't know what else to say or do and I guess I panicked. 

My regular customer doesn't seem like a creepy stalker person, more of a shy geeky type, but I really don't feel comfortable hanging out with relative strangers (even if I bring a friend). I don't even hang out with my co-workers outside of work-related events even though I consider most of them my friends.

I don't want to make it awkward by ignoring his/her calls and then having him/her come into my store the next day and having to make up an excuse ("My battery died." "I was in the shower." "Can't answer the phone when I'm raiding"). I also work alone a lot so I can't just disappear into the stock room or take a break when I see him/her come in.

And did I mention I'm in a steady relationship? Now that I'm thinking about it, I'm 99% sure I've talked about my significant other to my regular customer before ("I don't have Netflix but my significant other does." "Oh yeah, my significant other LOOOVES that actor").

Ideally, I would like to find a way of saying thanks but no thanks over the phone or text message without breaking his/her heart (even if the invitation was meant as a "just friends" thing) and making it super awkward when he/she comes into my store when I'm working.

Fingers crossed that he/she is not on Reddit.
<bot>: How do I sugar-coat saying "Thanks but no thanks. I panicked and didn't really want to hang out," after giving someone my phone number?