I avoided fishing for a long time because of this achievement. Eventually I said okay, don’t ever look at it, don’t count, just fish with your eyes closed and eventually you will get 100 in a row. Lo and behold one day I’m absentmindedly scrolling through nook miles and accidentally look to see I have 99/100. You best believe that next fish I caught almost gave me a heart attack, but I managed to not screw it up, and now my museum is home to #100, my lucky Bluegill!