ImageButton added to webview won't resize

ImageButton added to webview won't resize

I have a WebView that I want to add my own back button to, The webview is
one that has been set up specifically for viewing pdfs in app. I have
added the button and it works but I am unable to resize it or move it
around the screen, and as a result the pdf controls are underneath the
button and unusable. The button layout parameters seem to be something
along these lines (this is not in the code anywhere this is just what it
appears to be )
<ImageButton
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
/>
Here is the activity
public class PDFview extends Activity {
ImageButton im;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
Intent intent = getIntent();
String LinkTo = intent.getExtras().getString("link");
WebView mWebView= new WebView(this);
im = new ImageButton(this);
im.setImageResource(R.drawable.back);
im.setLayoutParams(new LayoutParams(100,100));
im.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
exitPDF();
}
});
im.setLeft(0);
im.setTop(200);
mWebView.getSettings().setJavaScriptEnabled(true);
mWebView.loadUrl("https://docs.google.com/gview?embedded=true&url="+LinkTo);
mWebView.addView(im);
setContentView(mWebView);
}