How to end things with a girl for not a great reason

I’m writing here because I need some advice. I matched with someone on a dating app a few weeks ago and we’ve been talking non stop for a few weeks. She’s a great person and we get on really well. Problem is that well I’ve been kinda catfished to a small degree. Obviously I knew from the photos on her profile and ones she’s sent to me that she’s not a skinny girl and a I thought was a lil chubby which I have no issue with. However she went out with her friends the other day and posted a picture and well in the nicest way possible she is veryyyy large. I know I sound like a terrible person for saying stuff like this but i don’t want to continue things as I feel no physical attraction. Told me friend and they said to just either block her or fizzle things out, I felt blocking was too rude so I went for the latter. I’ve been responding very slow and dry and now she’s message me asking what’s wrong. I’m not sure what to tell her ? I can’t just tell her I want to end things because she’s fatter than I thought I need some advice