ok does anybody know this book?

ok so this book ik the entire plot but for the LIFE of me i cant find the name of it anywhere. I would really appreciate it if yall out ther could help me out.

What I remember abt it:

-It is for the fifth grade reading level

-It is about a boy and his mom moving to a new town and him having to attend his grandfathers funeral, but it turns out later in the book that HE is his grandfather because of this door in the house they just moved into that sends whoever goes through it 20 years in the past. He continually uses it until he meets this girl during the ww2 era and starts dating her. He gets shipped off to the war but writes her constantly and then finds out she's pregnant. The girl, he later finds out, is his MOM, and he just impregnated his mom to have him. He goes crazy trying to continually turn back time and make his life right but it doesn't work. The book ends with him going so far back that he pops out of the door to when the house is being first built in the 1800's and then it ends with him helping out build the house.

- I believe the book had a blue cover where blue light shone from behind the door.

I would really appreciate it if anybody who knows the name of this book would reach out. Sorry for the kinda vague dump but I'm obsessed with figuring out what this book is. It is my fav book of all time. :3