The final match of the 2021 Championship will take place in Paris on Friday night with France hosting Scotland in a match which has been rearranged from earlier in the tournament.
France must win by scoring four tries and by a margin of 21 points or more if they are to wrestle the title away from current leaders Wales.
“We’ve got our fingers crossed. Although we’ve played some great stuff, we lost in Paris and it’s not in our hands,” said Williams.
“I’ll have to get a kilt on and support the Scots!”
Williams was a late call-up to the Wales squad for the Six Nations after his namesake and Cardiff Blues team-mate Tomos Williams suffered a hamstring injury.
He won his 32nd Test cap off the bench in the comprehensive win over Italy in Rome.
Williams was a travelling reserve for the dramatic 32-30 Welsh defeat by France which saw them fall just short of what would have been a Grand Slam.
But despite that result, Wales have still had a fine Championship whatever happens in the France and Scotland match.
Four wins from five and a record 20 Championship tries has been an impressive return.
“Wins are massive for a team and when I joined up after the Ireland match, it just gives you that extra bit of a kick,” said Williams.
“I was really pleased I went to Paris for the team and glad to be part of it.
“It would be great to get a winner’s medal. The boys worked so hard through the whole campaign and from what I’ve experienced, we deserve it.
“It would be great to see that work paying off.”
Williams was in Paris with Wales but flew straight back with the team on Sunday morning and produced an impressive performance as Cardiff Blues beat Edinburgh on Monday.
He set-up half-back partner Jarrod Evans for a try with one superb kick.
“I was a bit deflated after Saturday, but it was nice to get straight back on the horse, play a match, and win,” Williams said.
“It was fine. I’d been talking to the Cardiff boys throughout the weekend so I was up to date and it was quite seamless.”
