You are getting fucked dude.
I work in restaurant and started up front making barely that. Talked to BOH Manager and he put me on the Line and I'm getting $15 an hour, making overtime every week. If you aren't in the back, thats where you need to be.
As for you getting paid under the table, I can assume its because you are like 13-14 and cant legally work under the corporate rules. Better hope no on finds out or you will be out of a job.