A third consecutive two-under-par 70 saw him finish four shots behind winner Billy Downing, of Truro, who carded rounds of 68 71 67.
Hillsborough’s Joe Dean and Richard Law (Low Laithes), finished in a tie for 12th.
English men’s amateur champion Dean played his last two rounds in nine under, 67 68, after opening with a 78 while Law shot 69 74 70.
Burstwick Country Golf’s Joe Coyle (70 76 69) tied 19th alongside Lindrick’s Luke Jackson (74 71 70).
York’s Julian Taylor (71 73 74) placed 46th, Abbeydale’s Tom Perry (73 73 74) 66th and Hessle’s David Woodhead (77 71 73) 68th.
Eighty seven players made it through to the final round, each earning a minimum category 10 card on the EuroPro Tour, while the top 30 earn category 3.
McCarthy made a fine start by birdieing holes two and four as he sought to close a one-shot gap on Downing, but gave them back at holes six and seven.
A birdie at eight saw him turn in one under for the day, five under overall, and after bogeying 13 he birdied both 16 and 17 for his third two-under-par 70 in succession.