Don't approach it with the attitude that it's a waste of time, and don't assume you won't be doing or learning anything. Clinicals, in general, are what you make of them. I did 10 weeks of postpartum and L&D and never once had a mother or soon to be mother ask me to leave.
Be professional, be confident, and don't go in assuming they want you out of the room. Your instructors should be doing a bit of work upfront to make sure any patient you may have is receptive to students. When you enter the room, wash up while simply stating, "Hi, my name is __________, I'm the student nurse that's working with ________ today. I'm going to be doing _____________." Don't be shy, don't ask if they'd rather not have a guy, and be genuine in your desire to assist them in any way you can.
When not in the room, use the time to talk to the nurses about the uterine contraction strips and match them up to the fetal heart monitor. Learn about what early, late, variable decels look like, what they mean, what your actions are as a nurse without having to get a doctor's order. Ask to see interesting cases, try to see a delivery from both a primagravida and someone who has several kids already. Try to see a scheduled c-section and an emergency c-section. Participate in the nursery to do vaccinations, PKUs, bathing, feeding, and initial assessments. Tick off a postpartum mother by palpating her fundus and checking for beats of clonus. Learn your station, positions, possible complications of pregnancy and delivery and what S/S those produce as well as what nursing actions they require. Learn the underlying causes and reasons of medications used during pregnancy, preeclampsia, postpartum hemorrhage and prevention of hypovolemic shock. The list goes on and on about what you CAN be doing. Now, what you get out of it is up to you.