No, it's really not necessary to send recorded delivery which is expensive and, of course, the other person will have to sign for it, which could be a problem if they work. I can't imagine anyone would mark you down for this, though there's no pleasing some folk sometimes, so it would probably be a good idea to send them a quick email to explain and apologise in advance in case it causes them any inconvenience.
In future, just send ordinary 2nd class, but if you're worried about the book not arriving, you can get a proof of posting certificate at the PO, or even just get them to authorise your receipt - ask the person on the counter about it. That will entitle you to claim compensation for the value of the book if it goes missing.