If you could give us dimensions, that would help! Honestly, no judgement on you at all. A lot of well-intentioned, animal-loving people go to a pet store and are given information that is not intended to serve the needs of the animals but that company's bottom line. Even a lot of employees don't know better, and working in that environment really makes you want to believe what you're told.
Budgies can have very different personalities, and if you are choosing from a "budgie bin", at the very least it is a good idea to choose a pair based on which budgies are getting along (not just what they look like). So what you need to figure out before taking next step is whether 1) you have two budgies whose personalities are not ideally compatible or 2) if lack of space the main/only factor triggering bickering. As others have said, because female budgies can be territorial, they are especially sensitive to limited space. Age (have they hit budgie puberty? Has only one of them hit budgie puberty?) is another factor.
Asking here is a great start, I hope you continue communicating with us. If you are committed to providing a good life for your new companions, this forum is a wonderful resource.