Sorry it has not worked out the way you wanted it to, I sure you are upset about it. I just won't be upset at them to much in less they told you clearly it would be a 40 hour a week job. Sense 36 hours is considered full time, at least in the state of Florida and I'm assume in most states. I believe it's anything over 35 hours is considered full time, with benefits, when offered.

Maybe for a while you can get another part time job, till something comes along that you like, that will give you the 40 hours you want. Our you could figure out how much $ your losing from those 4 hours and ask for that much of a raise.