What are my chances of getting into a top 20 school without retaking the LSAT?
Pretty low. Please understand that I'm not trying to be harsh, I'm just answering your question directly. As I'm sure you've read here and elsewhere, law school admission is primarily a numbers game. GPA and (especially) LSAT are the two biggest factors in the process. For schools in the top 20, both your GPA and LSAT are on the low side. For elite schools like Harvard and Yale a GPA/LSAT combo of around 3.8-4.0/175-180 is common. Even at schools ranked in the 15-20 range I think you're looking at averages of around 3.5/165+.
Take a look at LSAC's admission profiles for more detailed info on individual schools. The conventional wisdom states that a high LSAT can help compensate for a lower GPA. In order to have a shot at the top 20 you'd probably have to retake and score very, very high (170+).
Will my job experience (including previous internships at prestigious places of employment) and scholarship outweigh my GPA and LSAT?
No, at top twenty schools your soft factors will generally not outweigh your GPA/LSAT. Your soft factors exist complimentary to, but not in lieu of your numeric qualifications. In other words, they're helpful, but not dispositive. The thing you have to keep in mind is that you will be competing against other applicants who have higher GPAs, higher LSATs, and
amazing soft factors. These schools tend to attract the best and the brightest, and literally thousands of people will apply for a handful of slots.
Also keep in mind that there is a big difference in the level of admissions competition at a top 20 school like Stanford versus, say, USC. If you raised your LSAT to 170ish you might have a shot at a place like SC, whereas the Stanford would still likely be out of reach.
Lastly, although this is probably anathema to everything you've read on every other board, don't get too caught up in rankings.
Remember, these rankings don't exist according to some provable law of the cosmos, they're just the subjective product of a magazine.
Some schools will always be elite because they possess a certain aura (Harvard/Yale/Stanford and a few others). Other schools that USNWR has deemed worthy of appearing in the "Top 20" are not really elite national schools so much as very reputable regional schools. Don't kid yourself into thinking that going to one of these places is going to open doors throughout the country based on pedigree alone. You may be better off going to a reputable local school instead.
With a 3.25/161 you can into plenty of good schools. Think about where you want to live and work, and go from there. If you want to stay in NC/Southeast region, it may make more sense to go to focus on getting a scholarship at a school like Wake Forest, NC State, UGA, or even Charlotte rather than a school that is simply ranked in the top twenty.