Just add a STYLE line and your progress becomes horizontal:
<ProgressBar
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/progress"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:max="100"
android:progress="45"/>