What industry are you in? In most engineering or software engineering or related white collar jobs the job market is still really tight.
They might be saying that jokingly or trying to tease you into standing up for yourself. Don't be afraid to move fast and break things - if you're a junior without responsibility it's okay to fuck up a thing every now and then.
They fucked up and gave you leverage. Brush your resume and threaten to walk unless they increase your pay to a Sr level dev, if they insist on you doing the work or creating and hiring for the role that can.
Start advocating for unions in tech work if you don't want to be exploited and put in a position like this.