"I can't go vegan because I still own some stuff with animal products in it."
An action is ethical or unethical regardless of what is in your house. The argument "I own stuff with animal products that I've already purchased" cannot be used in any way to logically counter the statement "Paying for unnecessary animal abuse is unethical". If the animal abuse that goes on in a slaughterhouse is unethical, that is true regardless of what objects exist in any arrangement in your house. So this wouldn't actually challenge veganism.
Veganism typically focuses on not purchasing animal products, e.g. I don't buy frozen chicken from my local grocer because that means they will order a new box of frozen chicken one bag sooner, and they will, in turn, increase demand at the chicken abattoir, which will call for an additional chicken to be trucked in sooner, so an addition chicken is bred, etc. up the supply chain. So it really is the consumption on that level that makes the biggest difference.
Whatever the case is, all deconversions of this type take some quantity of time. So even if you decided to go from carnist to ethical vegan overnight, you'd still have a pantry full of carnist food, etc. So this "scenario" is true for pretty much true for every former carnist that exists.
If you aren't convinced that you're a "True Vegan" unless you don't use any animal products, and you still own a pair of leather shoes (for example) that you want to wear out, then great - go vegan except for those shoes you already own. If you're convinced that not doing carnist things is more ethical than doing them, then just worry about that without labeling yourself a "True Vegan". The reason to go vegan isn't because you want some label of "Vegan" attached to you anyway; the reason to go vegan is because it is the biggest and easiest contribution you can personally make to the amount of animal cruelty that happens. So just do none of the carnist things moving forward, and don't worry about whether or not that one past purchase somehow spoils some imagined label in the future.
I'm sure that if you ask anyone that has been disabused of their carnism if they could go back and change the choices they've made regarding things they already own, the answer would (barring unusual circumstances) be yes. But we can't change the past, including that pair of shoes you bought. All we can change is the choices we make moving forward.