Emotions, Part 2

I just went to what was supposed to be an interview with a headhunter at a personnel firm for an engineering job.  They had me fill out the personnel paperwork, which I thought odd, but figured it was SOP.  While she was explaining the paperwork, the woman mistook me for a secretary.  I corrected her and she went on explaining everything.  As I was filling out the paperwork, and was halfway done, the lady came back in and said "Oh, you don't hafta fill that out.  Just come back tomorrow for an interview with your resume."  When I told her that was what I was told today would be, she vanished to talk to somebody and came back and said "just come back tomorrow."
It irritated me that I had wasted the gas to drive to the neighboring town to be told to come back tomorrow.  It angered me that they couldn't keep a schedule that they had set. It frustrated me that I had rearranged my schedule to be told "come back tomorrow."  It made me feel not worth their time and worthless. Instead of calling them on their horseshit (more than I already did), I just said thank you and left.  I'm still fuming.  I know the firm must generally work more with the nonprofessional fields, but you can't treat someone like that and expect them to be happy!  I was treated like drone number 2356896786346756, like I wasn't worth the lint on the bottom of their shoes.  I'm actually kinda angry at myself for keeping my professional cool and just taking it.  I know it's better for my career to do what I did, but I wanted to remind her that I drove 45 fucking minutes for an interview that didn't happen.  It made me feel shame, like it was somehow my fault they couldn't keep a schedule straight.  I felt worthless, like I was someone they couldn't be bothered with.  I felt that enough as a child, I don't need it from someone I just met.  It's really tempting to not go back.  If that's how they treat me now, how will they treat me in the long run?  I know I will go back, though.  I need that potential job.
I hate it when something like that happens.  Especially when I feel trapped into doing what they say, because my options seem limited.  I know I'm not trapped, that I could walk away and not go back tomorrow.  In the same breath, I don't feel I have an option, because this may be one of my few engineering job chances.
Gods, how I wish I hadn't screwed my resume.  I wish people were more understanding.  I wish people were kinder, and there were more smiles and fewer tears.  If wishes were horses, beggars would ride.
I also kinda wonder if maybe this is a hint from God.  Maybe one of those "quit trying to work around me and trust" moments.  I also know better  than to count my chickens before they've hatched. I've had promising interviews fail before.  Sorry, God.  I trust you, but I also know you can only help those who help themselves.
Well, God, the ball's in your court now.  I'm done with what happened earlier.  I'll listen for your small voice in me.  I really don't want to go back tomorrow, though.