第一句有重复.帮你改了如下.
I spent my summer wacation in the beautiful country .I went hiking with my friends by bikes.Although it was very dangerous,we had a good time.In the meanwhile ,we went swimming and fishing.The most interesting thing is that i went sightseeing and visited the aquarium.This is my happiest summer vacation!
恕我直言你这个语病和用词错的有点多,帮你改好了,纯手打.