Warning: Cannot modify header information – headers already sent by plugin

I created a custom plugin to display random authors on my blog. However, after I activated the plugin. I cannot login or logout anymore on my blog

I am also attaching my code for someone who could help. Apparently, my warning are as follows:

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-login.php on line 365

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-login.php on line 377

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 697

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 698

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 699

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 700

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 701

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 702

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 705

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 706

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 707

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 708

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 711

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 712

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 713

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 714

Warning: Cannot modify header information – headers already sent by (output started at /home/yoshi/public_html/wp-content/plugins/blogger_list/blogger-widget.php:1) in /home/yoshi/public_html/wp-includes/pluggable.php on line 881