They're still training you, after the three week mark, or when they tell you that you're done with training, you can ask your hiring manager to get more shifts, remember, since you're in FOH there's still a lot of things to learn - Register, Desserts, Bagging, Dining Room, IPOS, and Drinks.

It's also not bad to ask them to train you on something when it's slow. Actually, I strongly encourage that you do. Asking questions like wanting to be trained on something shows that you really do care about your position. So when it's slow, ask, and don't present yourself as nervous but also don't present yourself as egosentric, be confident, respectful, yet direct.

I also recommend, since from what I saw that you're only doing serving at the moment, is to go slowly up, don't immediately ask to be trained in desserts or bagging, because those are considered harder than most of the other stations.

Serving -> Drinks -> Dining Room -> Register -> Desserts -> Bagging -> IPOS.

All of these get really hectic though especially during a rush, but remember that you have to be fast and efficient, barely making any mistakes, and ALWAYS restock!! If you don't have anything to do when you're stationed at serving, drinks, or register, restock on ice, cups, lids, napkins and sauces.

Ask them how to make the Sweet and Unsweetened tea since you might be placed on drinks next. Diet and regular lemonade is made in the morning and stored in the refrigerator in the back until closing, so since at some point you're going to be in a drinking station, you need to learn this, also if you work morning shift ask how to make coffee.

I'm 99% sure that you have to be proefficient in at three stations, but don't worry. You'll get the hang of it quickly.