Good morning Neeraj,
The first thing you should do and always after today and that is totally define your sketches. You need to open up your first sketch and lock everything down with dimensions and relations. Make your horizontal lines horizontal and vertical, vertical.
That is where you need to start from
I have downloaded this part on the internet, I assumed it would be correct. Had I sketched it myself I would have probably fully defined the sketch, but I didn't notice until you mentioned it.
I will try to fully define the sketch and report back with my findings...
Set the Measure tool to report the maximum decimal places (8), and then select pairs of faces which should be parallel or perpendicular. You will find faces (even adjacent ones) which are supposed to be co-linear and horizontal, are not. The discrepancy is very small (0.00000170deg) but still enough to prevent correct SW mating.
are you sure its this part that is causing the issue?