The 19-year-old keeper has returned to Vicarage Road after spending just two weeks with the League Two side.
"Scott did really well for me and is a good keeper," Morecambe boss Sammy McIlroy told his club's official website.
"He had a great game at Macclesfield and did well against Bury in midweek for me as well.
"Watford were really helpful in letting us have him and I would like to thank them for their support."