I lied to my girlfriend for a whole year after I catfished her as my ex
Why would you pretend to be your ex?
I want to make her fall in love with me
That's deviously manipulative on your part. Just let things happen naturally or not at all. If you gf comes to know what you did , she's going to resent you.
*sighs* I'm gonna change, I promise.
You should come clean about your behaviour to your gf and should apologize. I hope you genuinely regret for what you did.