Help me Up

Ironically, yesterday the bartender that works Saturday afternoon, and has been at the Bar for 10 years, quit. A shift is open. I have to fight for this, but seniority is not on my side. I feel that I have earned the opprotunity to take a bartending shift through a year of hard work and going above and beyond for the Bar.
Every morning I arrive at work 20 minutes early. I finish the sidework that has been left by the night server and turn on the heat. Then I go to the office and print the specials for the day if they were not done the night before. I am the only employee that picks up this task. The others wait for the manager to do it when he gets there. Waiting for the manager means that the specials are being inserted into the menus while customers are there. By doing it before we open I am able to complete the task before any customers arrive.
After doing the specials I move on to the bar. I take the fruit out of the cooler or cut fruit as needed, turn on the bar TVs and speakers, pull the covers off the liquor, fill the sinks, and prepare the bar rags. By this time a customer has arrived and is sitting at the bar. I serve the customer(s) until the bartender arrives. She is always 15 to 30 minutes late for work. When she does arrive I receive no compensation for taking care of her first customers. During the next 3 hours I watch as the bar fills up and the bartender gets busy while I care for the 5 to 7 tables I will get for the day.
When I have been allowed to cover bartending shifts I always receive positive comments from the customers. They say I am fast and attentive. They also compair me to the other bartenders. The comparisons I am uncomfortable with because they usually say things about the faults of the other bartenders. It is also frustrating to hear that I am great at a job that I can not have.
So today and over the next few days I will be fighting for this shift. It is more than just being able to bartend. It is that I feel I have earned the opprotunity.
A little more than that, I have been trying to figure out a way that I can work less days and make the same amount of money. Being that I live in an apartment with no roommate I can't afford a cut in pay, but my full time work schedule is overloading me. I do not want to compromise school, just to work less days. If I got this bartending shift I could afford to work 3 days a week instead of 5 and have more freedom in choosing classes.
Wish me luck and I'd love to hear any advice anyone has!!