Either:
A) "Fair enough. Cheers for being honest, I was just keeping it chilled & fun. Good luck

"
B) Just move on.
Either way you just want to make it seem to her like it's not a big deal.
Girls will mostly gravitate towards guys that don't pay them as much attention because they want to get that attention. It's why every so often I'll go full on no contact with my girlfriend till she contacts me with the standard "baby where u atttttttt?

" then next time we have sex she goes full out, gets on top, makes sure she's at the height of her sexiness and such.
Keeping a girl interested isn't about being fullon asshole or fullon nice guy. You flip between the two. Keeps them guessing.
You also made plans WAY too far ahead which is boring to her and makes it seem like you don't have an active lifestyle. ANY PLANS you/her make ahead of the end of the week will most likely not happen. Even if she flakes and suggest a new date. Take the control back.
Her: Hey, I can't make it tonight

my friend is in town and I haven't seen him/her in ages.
Me: It's cool, i've been snapped up already. Have fun!
Her: Will do, maybe we could do something next week?
Me: Ah, I don't make plans that far ahead. Never know what's gonna pop up. I'll let you know when I know.
The other thing is that when a girl is doing ANYTHING apart from getting naked, sucking you off or bending over then it's just not a big deal to you. Your "I won't be playing the role of alternative" made it seem like it's a big deal to you. When the other dude is most likely going "Ah you're a free woman, have some fun" which she'll respect more and get naked for.
The problem with the majority of men these days is that they make themselves far too available as soon as a woman shows interest. The only time this develops into a relationship is when
A) She's a mental.
B) She's insecure (thus mental)
C) She does fuckall and thus isn't an interesting person and is only fuck buddy worthy (in which case she'll turn mental)