Bella, the length and width of the board seem a really good choice for someone of your size and ability. However, 19 inches is very narrow for a board that length. With boards that length, there are two kinds (in general) - mini mals, which have rounded noses and are usually 22 inches wide or so; and 'guns', which have pointy noses and much narrower (around 19 inches). The former are ideal for you, the latter designed as big wave boards (really big waves) and are not beginner boards at all.
Have a read of this thread and Jaffa's post about 3 or 4 down, and see the pictures.
viewtopic.php?t=18562If the board you are looking at is a 'gun' - you can tell from the pointy nose and tail and by how curved the board is when looking at it from side on, then I really warn against buying it.
what you want is 7'6" x 22" x 2 3/4", or something pretty similar
If you have more details about the board, let us know
EDIT: oops, beaten to it!