The stigma against double texting is an insecure schoolgirl affectation. Don’t worry about it.
Personally I detest chain-texts (a whole bunch of short messages in quick succession, like 8-10 or so) because a) I get the impression the writer didn’t want to bother organizing his thoughts before communicating, and expects me to do it for him and b) it makes my phone vibrate/beep a lot and it’s just distracting. But that is not what’s going on here. It’s just two texts with complete sentences.
TLDR: you’re fine, texting etiquette-wise. Double texting is not really a thing.
I prefer chain texts when I am engaging in a conversation. It feels more like natural conversation. As a sentence is out of my brain, the recipient has it. Sometimes the thoughts are fully organized, there's just a linebreak between them, and it's just a formatting distinction. But there are differences between "sending a text message to relay information" and "having a conversation via SMS"
The obnoxious part is the constant vibrate/beep per incoming message, but Android has a "minimum time between notification sounds" config option though, I imagine Apple does too, so that has never really bothered me either.
Your texts are formatted much better than most. I'm not sure what concern you have with the spacing (what, is there an extra space after the pluses? Meh). Double texting is very common. You're good, 8.