YOU SAID:

今まで見たことがないものがたくさんあります

INTO JAPANESE

今まで見たことがないものがたくさんさんあります

BACK INTO ENGLISH

There are many things that I have never seen before

INTO JAPANESE

私は今まで見たことがないことがたくさんあります

BACK INTO ENGLISH

There are a lot of things I have never seen

INTO JAPANESE

私が見たことがないものがたくさんあります

BACK INTO ENGLISH

There are a lot of things I have not seen

INTO JAPANESE

私が見たことがないものがたくさんあります

BACK INTO ENGLISH

There are a lot of things I have not seen