chance me for top 20 CS schools

If you’re low income, almost none of these schools will be affordable. Stanford and MIT might provide the best options at giving need-based aid, but that’s far from guaranteed. You stand a good shot at a scholarship from GA Tech. If you’re low income and you’re planning to study CS, then your best option would be to follow the money. Prestige is pretty much meaningless with computers and technology, so the best value for the money is going to be a scholarship. Compare offers and decide the best one.