gamertag wont change

so I just recently got the free minecraft windows 10 edition beta and an xbox account, as I was creating an xbox account it gave me a gamertag of diligenttea1464, I didn't really like it so I went to the xbox app and changed it but on minecraft it still shows up as dilligenttea1464 I tried re-installing but it wont work I'm guessing its a bug so I'm reporting it here.