Veli wants to show Peace with Sonic, with a Hug. But Sonic is being stubborn and still doesn't trust her.
This is also a image to have a size comparison. She is pretty small almost the same size as Tails.

But so that people don't get the wrong idea the only main reason why Sonic doesn't trust Veli is simply because in his point of view; how she can still be a Nightmare without Dark Gaia. Cause without Dark Gaia all the nightmares would've faded away yet she stayed which makes him suspicious. Add extra that she is Tails new friend and he worries about his best friends safety.