I have written the code of my question, but there are still some bugs and I can't figure out how to solve them. Pleaseeee help ! ! 1

# Guessing game 
# player guesses a random letter generated
# unlimited guesses

import random, string

def main():
    continue_game = True
    while continue_game== True:
        play_one_round()
        continue_game = play_again()
        
def play_one_round():
    # play one round of the game
    display_instructions()
    print('I am thinking of a letter between a and z.')
    
    # generate a random letter from a to z
    letter = random.choice(string.ascii_letters)
    letter = letter.lower()
    
    guess_num = 0   
    guess_list = []
    overall_guess_list=[]
    while True:
        guess = input('Take a guess: ')
        guess_list.append(guess)
        guess_num = guess_num+1
        if guess>= 'a' and guess<= 'z':
            if guess < letter:
                print('Your guess is too low.')
                continue
            elif guess > letter:
                print('Your guess is too high.')
                continue 
            elif guess== letter:
                print('Good Job, you guessed the correct letter!')
                answer = guess
                break
        else:
            print('Invalid Input') 
            continue
        
    print('---MY STATS---')
    print('Number of Guesses: ', guess_num)
    overall_guess_list.append(guess_num)       # total guesses of all games
    ranking_label(guess_num)
    worst_letter = worst_guess(guess,answer, guess_list)
    print('Worst Letter Guess: ', worst_letter)
    play_again()    
    
    
def display_instructions():
    # display  instructions
    instructions_file = open('instructions.txt', 'r')
    instructions = instructions_file.read()
    instructions_file.close()
    print(instructions)
    
def ranking_label(guess_num):
    if guess_num <5:
        print('Level: Expert')
    elif guess_num>=5 and guess_num<=10:
        print('Level: Intermediate')
    else:
        print('Level: Beginner')
        
def worst_guess(guess, answer, guess_list):
    diff_list = []
    for guess in guess_list:
        diff = abs(ord(guess)-ord(answer))
        diff_list.append(diff)
    worst_num = int(max(diff_list))
    worst_letter = abs(ord(answer)- worst_num)
    
    return chr(worst_letter)

def play_again():
    # prompt to play again
    # depends on player's choice
    again = input('Would you like to play again? Y/N ')
    if again.lower() == 'y':
        continue_game = True
    else:
        continue_game =  False
        print(summary_stat(overall_guess_list))
    return continue_game
    
def summary_stat(overall_guess_list):
    print('---SUMMARY STATS---')
    lowest = min(overall_guess_list)
    highest = max(overall_guess_list)
    print('Lowest number of Guesses: ', lowest)
    print('Highest number of guesses: ', highest)
    avg_guess = sum(overall_guess_list)/ len(overall_guess_list)
    print('Average Number of Guesses: ', avg_guess)
    if avg_guess <5:
        print('Overall Level: Expert')
    elif avg_guess>=5 and avg_guess<=10:
        print('Overall Level: Intermediate')
    else:
        print('Overall Level: Beginner')    

        
main()