Help me with this Python code
How can I remove the yellow area overflowing from some bins? This is the graph and the generatind Python code underneath.
import math
import numpy as np
import matplotlib.pyplot as plt
from scipy.optimize import curve_fit
from matplotlib.backends.backend_pdf import PdfPages
from matplotlib.ticker import AutoMinorLocator
from matplotlib.ticker import MultipleLocator
from scipy.stats import norm
%matplotlib inline
# ISTOGRAMMA
istogramma = np.loadtxt("20h.txt")
x = istogramma[:, 0] # centroidi
y = istogramma[:, 1] # conteggi
plt.figure(figsize = (6, 6))
plt.bar(x, y / 1000, width = 1,
color = 'none', edgecolor = 'none', alpha = 0.5)
plt.bar(x[303:320], y[303:320] / 1000, width = 1,
color = 'skyblue', edgecolor = 'none', alpha = 0.6, zorder = 1)
plt.bar(x[379:385], y[379:385] / 1000, width = 1,
color = 'skyblue', edgecolor = 'none', alpha = 0.6, zorder = 1)
plt.title('Spettro gamma da 20 ore\n', fontsize = 16)
plt.xlabel('Canali', fontsize = 14)
plt.ylabel('Conteggi ($\\times$10\u00B3)', fontsize = 14)
plt.xlim(294, 396)
plt.ylim(4, 9)
m = np.linspace(0, 4096, 4096)
b = -0.0425039 # pendenza
a = 21.1643 # intercetta
n = b * m + a
plt.plot(m, n, label = "Regressione lineare", color = 'crimson', linewidth=2, zorder = 3)
plt.step(x, y / 1000, where = 'mid', color = 'black', linewidth = 1)
mask1 = (m >= 321) & (m < 380)
# intervallo desiderato
mask = (x >= 321) & (x <= 380)
x_sel = x[mask]
y_sel = y[mask] / 1000
# bordi reali dei bin
left_edges = x_sel - 0.5
right_edges = x_sel + 0.5
# numero di punti per bin
N = 100
# array espansi
x_dense = []
y_dense = []
for l, r, val in zip(left_edges, right_edges, y_sel):
xd = np.linspace(l, r, N, endpoint=False)
x_dense.extend(xd)
y_dense.extend([val] * len(xd))
x_dense = np.array(x_dense)
y_dense = np.array(y_dense)
# retta liscia sugli stessi punti
n_dense = b * x_dense + a
# fill
plt.fill_between(x_dense,n_dense,y_dense,where=(y_dense >= n_dense),color='red',alpha=0.5,zorder=2)
plt.fill_between(x_dense, n_dense, 0, color = 'orange', alpha = 0.5, zorder = 1)
plt.axvline(x = 304, color = 'blue', linestyle = '--', alpha = 0.5)
plt.axvline(x = 380, color = 'blue', linestyle = '--', alpha = 0.5)
plt.axvline(x = 321, color = 'blue', linestyle = '--', alpha = 0.5)
plt.axvline(x = 386, color = 'blue', linestyle = '--', alpha = 0.5)
plt.grid(True, alpha = 0.3)
#plt.legend(fontsize = 14)
plt.tight_layout()
plt.show()