Wales began the tournament in confident mood, but have recorded just one victory in their current campaign but are determined to add the scalp of Italy alongside that of Scotland.
"We're obviously looking to finish the championship on a winning note," said Lewis. "We've got to give ourselves some confidence going into the World Cup. But we have to cut out the basic errors and mistakes from our game. You can't give away 20 penalties and expect to win an international game of rugby."
He added his side were frustrated as they have actually shown sporadic glimpses of the form which made them championship contenders last season.
"We have been our own worst enemies at time - our own mistakes cost us against Ireland. In the first half against France and Ireland we played reasonably well but didn't take it to the next level.
"The temptation could be there to change the way we play but we know that when it clicks we are a really good side. There are a lot of spoiling sides out there but we like to play attractive rugby. We just need to play the referees better and learn from our mistakes."
Wales Women v Italy (The Brewery Field, Bridgend, Sunday, KO 2pm)
Mared Evans (UWIC); Aimee Young (UWIC), Ceri Redman (UWIC), Naomi Thomas (Cardiff Quins), Non Evans (Cardiff Quins); Awen Thomas (unattached), Amy Day (Bristol Ladies); Catrin Edwards (Cardiff Quins), Rhian Bowden (UWIC), Jenny Davies (Waterloo), Gemma Hallett (Pontyclun), Rachel Taylor (Cardiff Quins), Catrina Nicholas (Cardiff Quins), Jamie Kift (Bristol Ladies), Mellissa Berry (capt, Blaydon).
Replacements: Claire Horgan (Saracens), Louise Horgan (Saracens), Claire Donavan (Saracens), Lisa Newton (UWIC), Louise Rickard (Woodbridge Amazons), Kay Rees (Harlequins), Caryl James (Cardiff Quins)
Tickets for the match are £5 for adults, £2.50 for Under 16s, and are available at the gate