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.