有冇錯 Gammer

Although I'm not the best but I'll try the best to do the best.
I suggest you put it this way:
Although I'm not the best yet I'll try the best to do the best. or
Although I'm not the best yet I'll try my utmost to be one.
你的句子是okay的, 但犯了英文兩大忌:
(1) Although 後不可用but, 應用yet.
(2) 太多重覆的字, 一句內包含三個best, 除非你在作詩, 否則, 應盡量避免.

you could also say:
Although I'm not the best, I will try to do my best.
"Although I'm not the best." 並不是一句完整的句子,
所以不可用句号,而是要用逗号,然後再連接上下半句,
使成為完整有意思的句子。
而之前的那位朋友已經說明了although 和 but 的 rules,
只要多注意就可避免用錯。
希望對你有幫助。

其實，你禁多句句子當中，是沒有一句是對的。如果你要寫，你應該寫成：Although i'm not the best,i will try my best to do it better.
因為如果你要片Although的話，你就應該不用but，而加逗號；但是如果你要用but的話，你就絕對不應該把although放在句子的前面。
總之，although和but是不可以一起用的！希望你明白這個道理啦！