Here is the full list of all 21 Last Day of June achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Wake Up.
Try to involve Teddy in the surprise.
Pick every petal of a single flower.
Give June a flower.
Prevent the crash caused by the Kid.
Prevent the crash caused by the Best Friend.
Prevent the crash caused by the Hunter.
Deliver the gift.
Prevent the crash caused by June.
Accepted the truth.
See the epilogue.
Open the gate to the Graveyard.
Look at every viewable in Carl and June's house.
Listened to every diorama.
Peek at Carl and June at the Lake
Shoot the ball at the basketball hoop four times.
Collect every memory of the Kid.
Collect every memory of the Best Friend.
Collect every memory of the Hunter.
Collect every memory of the Old Man.
Knock over four vases.