Keep Apple Watch awake

As for now that is not possible. The watch will lock when the user is lowering his/hers wrist or after a certain amount of time.

You can't keep Apple Watch awake programmatically. You can change the end-user settings in Apple Watch settings app or in the Apple Watch app on iPhone, but there is no way to do this programmatically and with coding.

The screen will be turned off after a certain amount of time (which is adjustable in Apple Watch Settings app, or in the Apple Watch app on iPhone), or when user lowers his or her wrist. You can't do anything in order to stop this, because it is one of the main and core features of the Apple Watch, which is the same thing in all apps ever made for it.