Now spend 60 percent of your time on the song isolating those mistakes and trying to perfect them one measure at a time. Some songs are so difficult you may have to go 1 beat at a time - but GOOD NEWS, you're investing your time here, not just spending your time. Every minute you spend untangling your technique, learning new licks and fingerings, eliminating breaks in tone is making hundreds of pieces in your future better. The more you do this, the less you'll have to do it in other songs. So think about that to encourage yourself to spend the time, and remember, you're not losing the time, you're investing it. When one measure sounds pretty good, go to the next problem area or measure. Skip areas where you don't have problems. When you feel about 70 percent of your time on this song is over (remember, you performed it straight though once already), stop working on the hard sections and repeating problems and now perform the entire song (that's the good sections + the 60 seconds you've been working on). Do this several times in a row, concentrating now not on fixing mistakes but on keeping the MACRO rhythm, which means not stopping no matter what and keeping the correct number of even beats in each measure. Now you have successfully covered the big picture (not stopping for mistakes, learning to handle mistakes without losing Macro-rhythm, performing) and the little picture (worked at perfection, eliminating errors). You have worked on the song as the mechanic (details) and the race car driver (performing) and squeezed out the highest learning curve you can for yourself. That should be your normal practicing regimen. And how to change it as the performance comes up? Next time.
You can ace a math or history test with 100% intellect. But intellect will only take you to the gate, not through it, in music.