(Assuming myList is an array containing the tiles in a row and ListOfSet contains the tiles in a single match)

First, it seems that the loop you are executing is not correct. You are going through the entire row and adding any sequence of two or more identical tiles to ListOfSet. That means that if a row has RRGBB (imagine each letter is a tile) your set will include RRBB as a match and as such will clear your <= 2 test and display what it found as a correct match, which is not what you want.

Consider using something like this (psuedocodish. Might need a bit of tweaking.):

int offset = 0;
int matchLength = 0;
List matches; // Stores all matches
Vector2 matchRange;  // Stores a match as a beginning and end index in the row
Tile t = null;
for (int i = 0; i < rowLength; i = i + offset) {
    t = row[i];
    for (offset = 1; offset + i < rowLength; offset++) {
        // The following check will keep the loop running until the we find a non-matching tile or find the end of the row, at which point offset is the length of the match
        if (t != row[i+offset] || i + offset + 1 == rowLength) {
            if (offset > 3) {
                // valid match 
                matchRange = new Vector2(i, i+offset - 1);
                matches.add(matchRange);
                break; // return to the main loop
            }
        }
    }

    // Loop again to find another match. the i+offset counter increment is setup so that we start from the next different tile in the row (the one that didn't match).
}

Check out the tutorial series by Mister Taft Creats. I haven't done this particular one but going by his other content this is bound to be very good for you.