[bazaroni]

1) The answer to that needs to come from you. If it's important to you to work at a "big four" tech company, it's probably possible with enough effort.

2) I think most people in industry realize that interviews don't really correlate well with how well people actually do their jobs. So I wouldn't take rejection too hard. It really is strange that in interviews we test for "can you figure out a non-trivial problem in the time it takes for me to eat a sandwich" when most software engineering roles are more along the lines of "can you work well with others, generate and document clean/functional code, and learn what you need as requirements change".

3) For most things, the best way to get better at something is to do more of it. Interview every single day. Hopefully over time you will get better at it. If you don't, consider seeking help with your performance anxiety. That might help.

Best of luck! :)