I have a similar story: coming straight out of undergrad and from Economics background. Thing is, 3 years ago I applied to US for undergrad and was rejected by all schools. Pretty devastated. Have set my heart on going to US for as long as I can remember.
Although most public policy programs say they admit less than 10% of the applicants from undergrad, who knows, you can be the one! I must stress that the biggest difference to my application now compared to 3 years ago is the personal statement. If you have a great profile but cannot communicate it, it's the biggest pity.
This is my final result:
Accepted: Georgetown MPP, Duke MPP, Austin Texas MPAff, UChicago MPP, Stanford IPS, UMichigan MPP
Rejected: George Washington MPA, Princeton, Harvard MPP