No problem. If you are happy with everything else then don’t exchange it. Also it’s worth noting that when you put things in the bag the flap can look slanted anyway, for example if there are more things on one side of the bag than the other. I have seen some really obvious examples of slanted flaps and they were way more obvious than yours. A lot of jumbos are like that. Most normal flaps look like yours.
Yes the ones I saw in store were crazy looking!! One of the flaps was like a half inch taller than the other despite it being crooked, and another was bent! That brought on my hesitation to try with another. Thanks so much, good to know even a perfect bag can be changed once full! Makes me feel way more reassured. ☺