The rank in General category can be calculated by the following formula

(100-Percentile score)*869010/100, Therefore your rank is 147123

If the number of student get increased to 1200000 then the rank would be

(100-Percentile rank)*1200000/100 ,which is 203160

as of now it is hard to tell your ST category rank and therefore the possible state college , meanwhile you can use JEE Main college predictor the  know the chances of college, link is given below

JEE MAIN college Predictor