Change in your mail.php
'username' => env('username i got from mailtrap'),
'password' => env('password i got from mailtrap'),
to
'username' => env('MAIL_USERNAME'),
'password' => env('MAIL_PASSWORD'),
The first parameter you pass to env() method is the config key, and not the default value. You could pass the default value as second parameter, likewise:
'username' => env('MAIL_USERNAME', 'your username'),
'password' => env('MAIL_PASSWORD', 'your password'),
What you have done is told your application to look for config with key
Hope that helps.