Week 9 - Challenge 3 - Bumper

I tried my best to complete this challenge as per the given question and according to the course videos but I failed after so many trials . I am submitting the challenge with the issues ,

It kept on giving this warning in the last trim which was required to complete the challenge .

And it keeps on showing these red lines every times I tried trimming the A-C Surface with B surface .

Please go through the CAT Part file , and if possible clarify the issue .