[Plugin: WordPress Simple Paypal Shopping Cart] Simple Shopping Cart installation won't let me

Help! I just unzipped and installed the Simple Paypal plugin and it gave me some weird message which I can’t duplicate as I now cannot get into my dashboard to deactivate it or delete it. It’s like I’ve been blocked from my own site. I’m not a power user and was just looking for a simple shopping cart plugin to start selling my shirts. Here’s the msg I now get when I try to log into my dashboard…my website is https://www.thedrbuffexperience.com. Thank you for your assistance!

Warning: session_start() [function.session-start]: open(/home/content/27/7631827/tmp/sess_lv8uadb89q68b8a11drn5ljd91, O_RDWR) failed: No such file or directory (2) in /home/content/27/7631827/html/wordpress/wp-content/plugins/wordpress-paypal-shopping-cart/wp_shopping_cart.php on line 22

Warning: session_start() [function.session-start]: Cannot send session cookie – headers already sent by (output started at /home/content/27/7631827/html/wordpress/wp-content/plugins/wordpress-paypal-shopping-cart/wp_shopping_cart.php:22) in /home/content/27/7631827/html/wordpress/wp-content/plugins/wordpress-paypal-shopping-cart/wp_shopping_cart.php on line 22

Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /home/content/27/7631827/html/wordpress/wp-content/plugins/wordpress-paypal-shopping-cart/wp_shopping_cart.php:22) in /home/content/27/7631827/html/wordpress/wp-content/plugins/wordpress-paypal-shopping-cart/wp_shopping_cart.php on line 22

Warning: Cannot modify header information – headers already sent by (output started at /home/content/27/7631827/html/wordpress/wp-content/plugins/wordpress-paypal-shopping-cart/wp_shopping_cart.php:22) in /home/content/27/7631827/html/wordpress/wp-includes/pluggable.php on line 881

Warning: Unknown: open(/home/content/27/7631827/tmp/sess_lv8uadb89q68b8a11drn5ljd91, O_RDWR) failed: No such file or directory (2) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct () in Unknown on line 0

https://www.ads-software.com/extend/plugins/wordpress-simple-paypal-shopping-cart/