Pretty sure if you clear the "Attach log file to email" checkbox in the Setting task, you'll no longer get the log on the email.
As for preventing the error message and code from appearing in the email, have you tried the "Use file for body" checkbox option under the Compose Email button. I have not used it before, but it might suppress the default body of the email and replace it with the contents of the file. Possible it might still write the error/code info below your form, you'll have to try it out to see. You might also change the logging level to Basic if you have it as Verbose, but it will also limit your log itself to Basic info.
See help topic Automate Sending Email. Another help item is Automate Find and Replace, if you want to customize the email body file to add variable info.