The winger underwent surgery on his knee before the start of the tournament, but he now feels on top form.
"I do feel I'm back on song again," said the 24-year-old.
"It does take a few weeks to get back into it, even though you deny it. It naturally takes a few games to get used to running around and being in position again."
Ashton's three scores against Romania took his Test tally for England to 14 in 16 games.