ジャスミンさん、
こんにちは!
Actually, if you're translating stand-alone sentence, your Japanese was perfect!!
I bet the book has certain context behind. Is it one sentence only or does it have pairing sentence (or is it
a conversation)?
Both your sentence and book's sentence are grammatically correct, but the meanings are a bit different.
Your sentence is, as I wrote above, correct and I believe you don't have question there.
The book's sentence, however, needs some "accompanying sentence/situation".
If this person eats only a bit of bread, AND eat something else, the book's sentence is proper.
For example, imagine you're at lunch table, and there're bread, salad and meat on the table.
You don't want to eat meat now, as you feel like salad.
パンは、すこしだけ 食べます。 As to bread, I eat only a little bit.
サラダは、たくさん 食べます。 As to salad, I'll eat a lot.
にくは、食べません。 As to meat, I won't eat.
Hope this helps!
Natsuko(奈津子),
Team JapanesePod101.com