The simple answer is that you are BELOW the G-line. You are not guaranteed a line.

I know it is infuriating to see a junior pilot receive a line and you get reserve. The most likely case is that the junior pilot had some type of credit already on their line (vacation, training, carry in) that made it easier to construct a legal line with the remaining trips available. Most likely, those same trips would not build you a legal line. You can always file a PBS dispute but your cards have already been dealt. Sometimes you win, most likely you will lose (but you get some cockamamie excuse as to why you couldn't get a line). All of this is perfectly allowed under the UPA.

Once you are ABOVE the G-line you are guaranteed a line. No need to waive anything (it could help, it could hurt also).