Never apply malice when stupidity will suffice.
I, too, am a shy person and homeschooling forced me way out of my comfort zone to find friends for my kids. I am not going to lie, it was a few years before I found some peeps. I kissed a lot of frogs.
My suggestions based on what you posted:
If you say you would like to see X movie and they say yes pick a date right then and there. Do not leave it open ended with a let me know when would be good for you. Once plans are made follow up with a text a few days before. A quick and breezy "looking forward to seeing X with you on Tuesday"
Cancelation - immediately reschedule. Do not leave a loose end hanging out there.
For me, I found I really had to work hard to help my kids make connections.