I have flat nipples. I didn't know a thing about this when I went to give birth. And she couldn't latch on. So I ended up giving formula to her in the hospital. The staff there were too busy to help me properly with the first steps of breastfeeding.
So my advice is to be prepared. Take the shield (as others said). But also take a pump (read the instructions first... I didn't, and it was extremely overwhelming to understand how to pump, once I had a crying newborn on my side) with you, or learn how to hand express before you go in. Take a small spoon or syringe with you as well, that you can express into/onto and you can feed the colostrum to the baby. The first couple of days only a couple drops of colostrum comes out and it is enough for the baby, because it's full of nutrition.
I couldn't breastfeed at the end, as she was lazy to suck and I had very slow flow and even with the shield on, she fell asleep before getting enough and she wasn't happy about it. So I ended up pumping and bottle feed (mix feed, due to low supply). What I found, that after a couple of weeks of pumping, my nipples actually became pronounced. And she did manage to latch on properly. But due to her impatience and my low supply, breastfeeding still didn't work out.
I am only telling you my story, so you know, there are lot of factors... and you may not be able to breastfeed, however hard you try. And it is OKAY. Don't feel guilty or sad. Do your best. Pump if you want to, or feed formula. Fed is best!
I wish someone would have told me these things before I gave birth. I had a terrible first month because of moms guilt and constant crying at the breast.