Modify iframe for application form in psy390.md

Updated iframe size and added center alignment for the application form.

Author: mcoverdale

docs/joinus/psy390.md

@@ -12,6 +12,6 @@ Students will be involved in all phases of research, including designing experim
 
 Our lab is currently full for the Spring 2026 semester.  Applications will reopen for Fall 2026 in mid-to-late February.  Thank you for your interest.
 
-<p>
-<iframe width="700px" height="480px" src="https://forms.office.com/Pages/ResponsePage.aspx?id=Ob0wQVN8nEGx5YdY1tY_IT6cdtoXKcJGrmrbuOquBXFUN0ZDRThJMkhBV0VaQVQ3TURMMEtWMzBFSS4u&embed=true" frameborder="0" marginwidth="0" marginheight="0" style="border: none; max-width:100%; max-height:100vh" allowfullscreen webkitallowfullscreen mozallowfullscreen msallowfullscreen> </iframe>
-</p>
+<p><center>
+<iframe width="700px" height="900px" src="https://forms.office.com/Pages/ResponsePage.aspx?id=Ob0wQVN8nEGx5YdY1tY_IT6cdtoXKcJGrmrbuOquBXFUN0ZDRThJMkhBV0VaQVQ3TURMMEtWMzBFSS4u&embed=true" frameborder="0" marginwidth="0" marginheight="0" style="border: none; max-width:100%; max-height:100vh" allowfullscreen webkitallowfullscreen mozallowfullscreen msallowfullscreen> </iframe>
+</center></p>