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I'll second what the others are saying about not closing the card. No other issuer, that I am aware of, will allow you to expontentially increase your limit so fast. I was bummed when I got my first Amex as well and saw the starting limit. I applied in May 2017 and received a 2k limit. Six months later amex gave me a auto-increase to 6K. A few weeks later I decided to try my luck at the 3 times credit limit trick. Amex auto approved my request to increase my credit limit from 6K to 18K. From there I went to 32 or 34K and now the card is sitting at 48K. Give it a chance, put usage through it, pay it off repeatedly if possible, and the rest will work itself out.
Congrats on your approval !!!!!