Remedy this by adding fertilizer...and often and TONS of water in the summer. They take off in the heat when they get water and nutrients. That will probably help your fruit to enlarge.

What is you current watering and fertilizing schedule....and where do you live?

M.A.D.

they like a lot of nitrogen and organic matter.
and, while i would water fairly often when its very hot,
it really depends on the type of soil also.
if the soil doesnt drain well, and the soil is moist/wet -
i wouldnt water.

you want the soil to be moist, but not wet.
if its mulched well, thaat reduces the need for frequent waterings also.

you can add epsom salt also.
i give mine 1 teaspoon a month in the water
and foliar spray with epsom once a week.

fish, worm castings, chicken poo are all good organics to add.
mulch heavily, but leave a few inches near the trunk open.

if you want to use chemical ferts
i would normally say use what i use
KGRO 24-8-16 (high N) it has lots of micro-nutrients as well
but, since it has fruit, you may want to cut back on the N, and use something balanced

I have been giving my papaya tree all the scraps from making fruit smoothies.

By pureeing the scraps and mixing with water have an endless supply of nutrients to feed it. Once dried turn it under.

Climate plays a big role in developing papayas

This was my Red Lady Papaya tree last year four months after planting.

it does take several months for the fruit to rip[en by the way...

wait till there is at least some yellow on it

or, better, is mostly yellow and turning soft.

most papaya seeds are %66 chance that it is a perfect flower

(hermaphrodite). it depends on variety, but, there are male, female, and herm trees.

then, there are some trees with all 3 types of flowers on them.

papaya sex is strange, but, normally,, you do not need another plant.

It also depends on if you have it in a pot or planted in the ground. Potted plants seem to have small fruit.