在国外买东西时不想要了该怎么说啊?

I will not, thanks.
我不要，谢谢。
Not for me, thanks.
我不要，谢谢。
Thanks all the same, but I will not.
谢谢，不过我不要。
Thanks you, I do not want the anything yet.
谢谢，我什么也不要。

i am sorry that i don't want it any more.

i am sorry that i don't think it fits me.

i am sorry that i don't think it looks good on me.

直接说,I don't like it/I don't want it.外国人很直接的