Battery

First, make sure your iPhone and Watch have the latest software updates. Next, try resetting your watch by pressing in the crown and side button until you see the Apple logo, then release both. Next read this, it might help.....https://www.apple.com/batteries/maximizing-performance/

Additional to julieda’s comments, it is very likely battery life will improve when you get past the new toy stage and use the watch more normally with probably less screen usage (a big battery consumer).