By default plaintext emails are wrapped at 70 characters to enable as many email clients as possible to read any emails received. If you are certain that all recipients of your wppizza emails can read emails at a different linelengths, you can force the required length by adding the following 2 constants to your wp-config.php

define('WPPIZZA_PLAINTEXT_MAX_LINE_LENGTH', 128);/* non textarea form fields */
define('WPPIZZA_PLAINTEXT_MAX_LINE_LENGTH_WORDWRAP', 128);/* textarea form fields */

somewhere before
/* That's all, stop editing! Happy blogging. */

where 128 would equate to setting the maximum linelength to 128 (instead of the default). Change that number to use the maximum linelength you wish to set.