create a new emacs minor mode with custom C-RET binding

my-temp-mode.el

(defun my-temp-func ()
  (interactive)
  (insert "tempura true"))

(define-minor-mode my-temp-mode
  "throwaway minor mode for test"
  :lighter " TEMP!"
  :keymap (let ((map (make-sparse-keymap)))
            (define-key map [(control return)] 'my-temp-func)
            (define-key map (kbd "C-c f") 'my-temp-func)
            map))