Experts and BHG readers answer.
Fruit is too small
Fruit size is affected by a number of factors. The major one, however, is the genetics of the variety. If it's a small variety to begin with, there's little that you can do to enhance it's size. The other major thing affecting fruit size is crop load. If the tree has a heavy load (i.e. many fruits), each individual fruit will be small. Sometimes thinning out some of the fruits will make the others grow larger.