Me [22M] with my Girlfriend [19F] of 5months, is frequently unreliable and it's irritating me. Am I overreacting?

Mostly when it comes to following through with plans. If it's ever an emergency she's usually pretty good about it. She just has a habit of making plans with me and then not following through or being on time and it's starting to frustrate me to the point where I can't be bothered to hide my frustration.

For example. Last night I asked if I was going to see her today. She told me that I would and all she had to do were some house chores but she'd let me know when she wakes up and I could come over while she was doing them. I told her I'd help her out so we could have time to do something fun. I had to stay up a little later to finish some chores of my own and told her to just call me when she starts so I don't over sleep and follow through with my offer to help. I wake up this morning closer to noon and didn't have even a good morning text. I call her thinking maybe she just slept in too and she answers. It was pretty clear she'd been up for a few hours and had apparently made plans to go out with her dad and new girlfriend after she woke up. It's been about 4 hours and it's mid afternoon now and there's still no definite time for meeting up.

She has a habit of doing this. We live close. It's literally a 10 minute drive on surface streets. She'll tell me she'll come over at 11 and won't show up until 1. Or tell me she just got home and has to change her clothes before she meets me somewhere and won't get there for 2 or 3 hours.

I've told her how annoying it is for me to get stuck waiting for an unknown amount of time when I could be doing something else. She does these things and literally doesn't think about why it annoys me. It gets to the point where I'll end up being short on my texts because I honestly don't want to talk to her and am only replying so it doesn't get blown up into some big fight. It's starting to feel like my time isn't valuable. It's not unheard of for us to plan to spend a day together and doing things outdoors or w/e and then it's 5pm before she follows through and I spent half a day waiting and then at 8 she has plans with her mom or her sister. On those days if I had known it was going to be like that I'd have literally just told her not to see me. It's too late to go do anything we planned to and we'll spend most of the time figuring out what to do now and then not having enough time to do anything except get dinner.

We went to a party friday night through one of her friends. She knew everyone there and I didn't know anyone. I had girls all over me asking me to make plans to hang out with them and stuff with like specific dates and times. I'd never cheat and I think it's inappropriate for someone in a relationship to spend time with the opposite sex like that but part of me is starting to think like it'd almost be less frustrating to just be single. I love the girl to death and I honestly want to see her in my future because when we're together we're beyond amazing. Her whole family and all her friends call us "relationship goals" and come to us as an example of how a relationship should be and stuff but this one thing is just starting to really fucking irritate me.

TL;DR: Girlfriend is unreliable as fuck. Never on time and is hard to get to follow through without delays for plans. Really love her but I've started thinking about how being single would be less stressful. Am I overreacting?