A US dollar bill from 1957 is, indeed, worth more than its face value, but to find out precisely how much more, you should visit a numismatist. After some online research, it appears as though there is some disagreement as to how much a 1957 dollar bill is worth. According to one source, it is as little as $2, as it was a fairly common note, but someone else claimed that it might be worth as much as $35. A lot depends on which series the bill is from, such as series 'A', 'B', etc. I also found a $1 bill from 1057 in UNC condition, on sale on eBay for $2.59.
A lot depends on the condition of your note. If it is in uncirculated (UNC) condition, it should be worth more than if it has been circulated and if it is torn, or tattered at the edges. I recommend that you take your bill to a store that sells old currency and stamps, as a specialist should be able to give you a more precise figure.