Small game UI improvements

src/screens/Game/components/GridComponent.js

         return (
             <View style={{
                 aspectRatio: this.props.width / this.props.height,
+                borderRadius: 4,
                 ...this.props.style
             }}>
                 {this.getGrid()}

src/screens/Game/components/Preview.js

             style={{
                 marginRight: 5,
                 marginLeft: 5,
+                marginBottom: 5,
             }}
             key={index.toString()}
         />;