Why are my white nectarines 2 connected and not round?

Question

My white nectarine tree has double fruit and are small.

Answer 1

Usually, this is caused by malnutrition, but can also be caused by insect damage, or infections depending on exactly how it appears. Without seeing it would be hard to say.

In the meantime, this collection of articles will help you to grow these trees: https://www.gardeningknowhow.com/edible/fruits/nectarines