It's a date?

File: IMG_1780.jpg (38KB, 600x494px)

38KB, 600x494px

I met this girl last winter and had minimal interaction through the semester other than her coming to a party my friends held. I was currently dating somebody during that time so we just exchanged hellos. Over the summer I saw and made small talk with her at new student orientation events for our respective clubs.
I texted her and asked her to come to Shakespeare in the park play with me and she agreed. I said I'd bring wine if she brought a blanket and scheduled to get lunch beforehand.
The play is tonight and she texted me this morning asking if it was cool to invite one of our mutual friends. I thought it was pretty clear that it was a date but apparently not? I responded with "Sure" but within a minute I texted back "Actually I was thinking of it more as a date" and she responded "Oh! Ok!".
I'm 21 and have been passive enough in my dating past to not just sit through something I don't want to do. I just want to be really clear about tonight without sounding like a dick.
Should I respond anything else? I think I'm just gonna text her "haha, so still on for later?"