Meditation is much more than repeating a mantra. When one is properly instructed in how to meditate, guidance is provided on how to deal with other thoughts and feelings including thoughts about the mantra and the urge to open one’s eyes.If your yoga teacher has given you general instruction in these matters and you need additional assistance, then you should contact him or her to get clarification. If your yoga teacher has not given you formal instruction, but only told you to say a mantra, then you should seek out a qualified meditation teacher and get the full instruction that you need to meditate correctly.