1. Press harder and go more posterior on the globe....You can't be shy with scleral depression when you are starting out. If you are too timid, you will never see anything because you will not be indenting the eye enough. Tell the patient it is going to be uncomfortable/hurt, because it does.....Do it to yourself if you don't believe me.
2. "Practice" on soft eyes. Premie eyes get soft quickly on depression, so if your peds person does neonate exams, ask if you can do a couple with them(make sure the babies are healthy enough!)...A better option would be go with your retina specialist to the OR and ask them to allow you to depress after they have just done a buckle. Although the view will be horrible, the eye should be soft and easy to depress. This also has the benefit of not causing the patient pain as they were probably blocked/anesthetized.
If these don't work I suggest you ask your friendly retina specialist for some help because they will be able to offer both good advice and plenty of patients who need to be depressed.