It doesn't make you a bad person. But it does show that you didn't do sufficient research about guinea pigs before buying them.
Pigs sold in pet stores come from breeding mills, where sows are kept continually pregnant until they're too old to breed, and then they're killed. They're inbred, and often sold sick, mis-sexed, with parasites, and the baby sows are pregnant. They are shipped in horrible conditions. To the pet store, they're just another item to be sold, so when you buy two, they order two more to take their place. You participate in that whole atrocious chain when you buy a pig from a pet store.
On the other hand, when you adopt a guinea pig from a shelter or rescue, you give a home to a homeless pig, and you free up a space for another homeless pig to be taken in.
Do the pet store pigs deserve loving homes? Of course. But there's no end to it. Your "saving" one pet store pig just means another one will be deliberately bred. You save one, you condemn another one just like it. "Saving" a pig from a rescue or shelter doesn't have the same problem.