My house isn’t small, but when everybody is hereome, all I can do is stay in my room. My house isn’t small, but when everybody is home, all I can do is stay in my room.

It wasn't a complete sentence.

My house isn’t small butexcept for when everybody is here. My house isn’t small except for when everybody is here.

All I can do is stay inside my room.

I've added this to the other sentence to make it a complete sentence.

I can have my home backthe house to myself! I have the house to myself!

Finally, everyone in my house is gone jusbut me left. Finally, everyone in my house is gone but me.

Or you could say, My family (or whoever is living with you) finally left, and I'm home alone.

Finally, everyone in my house is gone just m's gone from my house, and I'm the only one left. Finally, everyone's gone from my house, and I'm the only one left.

NBut now I can do whatever I want. But now I can do whatever I want.

"but" contrasts with the previous sentence better.

I don’t need to go to the library, gym…the gym, etc. I don’t need to go to the library, the gym, etc.

I don’t need to go to the library, or the gym… I don’t need to go to the library, or the gym…

I can do all thatose things in this house, and no one will be in my way. I can do all those things in this house, and no one will be in my way.

I can do all that in this house and no one will get in my way. I can do all that in this house and no one will get in my way.

That is the best chaChristmas present I get've received! That is the best Christmas present I've received!

That is the best charismas present I could ever get! That is the best charismas present I could ever get!

"best present I could ever ask for" is another expression one can use here.