At least you got understanding of what N-400 interview is like @Roxy&Ryan
Thank you for the detailed experience here.
Technically, you can still travel with 2 year GC and extension letter. However, even with 10 year approval put aside, airlines sometimes don't know what to do with extension letters and deny boarding. If you fly, you should pick a big airline and big airports. I cannot give 100% guarantee you'll have no issues, but usually it's OK to travel