Android : How to center and change the size of my seekbar thumb?

I've tried to implement my custom seekbar design but when I use it, the seekbar is few pixels back from the actual position and also is pretty small. This is my layout for it.

<SeekBar
        android:id="@+id/seekBar"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:thumb="@drawable/bodka"
        android:indeterminate="false"
        android:layout_above="@+id/exit" 
        android:layout_alignParentLeft="true"/>

how can i fix that ?