Continuity mistake: When Peter and MJ hug on Tower Bridge he gets some blood from his face onto the left shoulder of her jacket. From other angles there's no blood.
Continuity mistake: SPOILER - The wounds on Pietro's body change. The most noticeable one is on his right shoulder. The amount of blood decreases too.
Factual error: When the action moves to England after the failed award ceremony, the British Union Flag hanging from the wall is upside down. The broad white band should be at the top left (nearest the top of the flag pole).
Other mistake: On one of the SHIELD monitors, "perimeter" is spelled "perimiter".
Continuity mistake: At the school, when Scott's suit is malfunctioning and he's big in the janitor's closet, his head is tilted towards his right shoulder. When Hope is working on the suit, we see Scott's head is now tilted towards his left shoulder, even though he's stuck and wouldn't have been able to move around like that. But in the next shot it's back to his right.
Continuity mistake: As Captain America arrives in his car at the airport car park, he stops right next to the line dividing the spots. In the following shot, when he steps out, the car is further away from the line, more towards the center of the spot. (01:26:50)
Continuity mistake: At the wedding, Christine tells Stephen something quite hurtful; wide-eyed, he asks her how long did she have it in the barrel; a black partygoer walks behind him but is gone in the reverse shot. Moreover, she replies "Long time" and a couple walks past her, only to walk again past Stephen in the next shot.
Continuity mistake: During the opening scene with Ego and Quill's mother, they run into the woods behind the Dairy Queen, and mom is wearing boots with fur trim. When they get to where the Ego's plant is in the ground, she is suddenly wearing sandals.
Continuity mistake: When the Dark Aster enters the atmosphere at the end of the film, its wings untwist as it descends, in most of the scenes afterwards and the hologram the ship's wings are still twisted, then later during the battle they untwist again.
Continuity mistake: In Riri Williams' dorm room, the number of braids hanging over her shoulder changes frequently while Riri and Shuri are talking.