I am currently making a custom keyboard for iOS 8, and I came across the problem that it is impossible to type. I found that you have to be far too accurate and press your finger exactly on the keys. This is obviously not the case for the system keyboard, as no matter where you type, some key gets pressed.
So my question is, how would I go about implementing a feature like that?
This likely relates to your tap zone. I believe for buttons Apple has firm recommendations for size in the Human Interface Guidelines. You will likely need to make the zone as large as possible without overlapping with neighboring buttons.
https://developer.apple.com/library/ios/documentation/userexperience/conceptual/mobilehig/