How to determine which is the nucleotide sequence of a gene?
You run a blast of your sequence. Then explore the results and you'll see somewhere that says "strand"  and is indication whether is plus/minus.

https://blast.ncbi.nlm.nih.gov/Blast.cgi

Also blast has a graphical interface in which you'll clearly see the matching and non-matching bases. Therefore it should help you to identify the differences between the 2 sequences.