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You should not apply to AMEX you will most likely get denied.
You should get another secure card too that will graduate and grow. I would recommend the below secured cards that can grduate and grow nicely.
NFCU (If you can get in)
Disocver
BofA
I was recently approved for the Delta card with as 619 EX FICO but as everyone said, I would wait it out a little until your scores are above 650 to improve your chances. Good luck!