Switch your primary musical thinking from right/correct to natural/comfortable. Practice a song, a measure, a lick, until it feels natural, until the RIGHT thing to play/sing is the thing your hands (or voice) want to do naturally. This also means you'll probably spend more time on less material. If something feels unnatural, it probably is! Don't ignore your body telling you it can't play/sing this part right here (and here and here). Rather, those bumpy areas are your targets for practice and perfection, for developing comfort, ease, and SKILLS. Stay with the problem area (2 notes/2 measures) until your hands/fingers relax. You may need to change how you physically are performing something to make it flow. And stop allowing yourself a pass to pause. "I almost missed this part, but fortunately I stopped for 2 beats and figured it out". WRONG. Pauses are your enemy; it's your body telling you 'I don't get it'. Slow down, repeat the offending area indefinitely until it's slow and smooth, sans pauses. Pauses are land mines waiting to blow up at your senior recital, your sister's wedding, your gig opening for One Republic. Your investment in the physical perfection of your musicianship will produce ever-widening areas of amazing skill. You'll also feel much more comfortable and confident as you perform.