OpenCV - Find subcontour in a contour

Question

i want to use the OpenCV Match Shapes-Function to find a known Contour in a larger image like in this example (3. Match Shapes)

https://docs.opencv.org/4.x/d5/d45/tutorial_py_contours_more_functions.html

The problem is that I do not know the complete contour, but only a part of it. In the attached example, for example, it would be only a quarter of the star.

Hier is an example code

import cv2 as cv
import imutils
import cv2 as cv2
import numpy as np
from matplotlib import pyplot as plt
plt.rcParams['figure.figsize'] = [30, 15]

img = cv.imread('lala.png')
org = img.copy()

img_grayscale = cv2.cvtColor(img, cv2.COLOR_RGB2GRAY)
ret,thresh = cv2.threshold(img_grayscale,25,255,cv2.THRESH_BINARY)

#find sub contour
mask = np.zeros(thresh.shape,np.uint8)
mask[330:550,3:172] = thresh[330:550,3:172]
contours, hierarchy = cv2.findContours(mask,cv2.RETR_TREE,cv2.CHAIN_APPROX_NONE)
plt.imshow(cv2.cvtColor(mask, cv2.COLOR_BGR2RGB)), plt.show()

cv.drawContours(img, contours, -1, (0,255,0), 3)
plt.imshow(cv2.cvtColor(img, cv2.COLOR_BGR2RGB)), plt.show()


#find all contours
ret,thresh = cv2.threshold(img_grayscale,25,255,cv2.THRESH_BINARY)
all_contours, hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_NONE)


#find match
ret = 1
for cnt in all_contours:
    ret_new = cv2.matchShapes(cnt, contours[0] ,1,0.0)  
    if ret_new < ret: 
        ret = ret_new
        matching_contour = cnt

cv.drawContours(org, matching_contour, -1, (0,255,0), 3)
plt.imshow(cv2.cvtColor(org, cv2.COLOR_BGR2RGB)), plt.show()

Do you have any idea how I can solve this? The Contour Matcher does not seem to support this function

Sub-Contour This shows the sub-contour, which i will find in a larger image with whole contours. The problem is the contour on the edge of the mask i think.

The whole image This is the whole image in which I have to find a choosen sub-contour