In the three games the Hornets have had Cathcart in their defensive ranks they have conceded eight goals, and the 20-year-old gave away a penalty in their 4-0 defeat to Cardiff last Saturday.
Yet Cathcart, who is highly rated at parent club Manchester United, hopes his future form will earn him a Northern Ireland call-up.
"It is going to take a while to settle in with new players and other things like that," Cathcart told the Watford Observer.
"But as I get my fitness back and play more games then I will improve and the team will improve as well.
"If you look around the Championship there are quite a lot of Northern Ireland players in it and there are scouts at all the matches, so I will be going out there to impress them as well."