If you do not want to create your own button component, a quick and dirty solution is to wrap the button in a view, which allows you to at least apply layout styling.
For example this would create a row of buttons:
<View style={{flexDirection: 'row'}}>
<View style={{flex:1 , marginRight:10}} >
<Button title="Save" onPress={() => {}}></Button>
</View>
<View style={{flex:1}} >
<Button title="Cancel" onPress={() => {}}></Button>
</View>
</View>