<em>[The following is how I might have written your entry. I am guessing that the town is one that you are returning to after a six year absence:]</em>

I have a three day holiday this weekend.

So, I'm going to go on a bicycle trip to a town where I have not been for six years.

It resides 120km from my home, and it will take approximately 7-8 hours.

I am concerned that my legs may get so tired-out and sore that I will have a very hard time riding back home!

<em>[Enjoy your trip (旅行をお楽しみください。), even if your legs do get a bit sore (痛い下脚を取得するにもかかわらず。)!]</em>

my trip by bicycle

I have a three days holidays this weekend.
So, I'm going to go on a trip to the town where I had been for six years by bicycle.

"where I had been for six years"   Not sure what you mean by this. Is this where you live? Is it where you go on vacation?

It is 120km from my home to there, and it will take 7-8 hours.
I am afraid of getting my legs hurt and not being able to go home.  Another phrase for "I am afraid of" is "I am worried about".

This is pretty well written. Good luck with your bike trip!  がんばってください！