I don’t think you’re grasping me here.
Atheists live their lives in ways very similar to yours. We love our spouses, kids, parents, friends. We have interests and hobbies that we love. We have jobs that we (hopefully) love. Most of us who are lucky enough to have been born in a first world country have pretty nice lives, and those of us with problems have problems no worse than anyone else’s.
Now, religious believers claim that there is some (presumably) “supernatural” source of love. Maybe you’re right, but obviously atheists don’t think you are. Yet, despite disagreeing with you, atheists are more than capable of the same love that you are.
Sure, you can say, “Oh! But if only you believed in my God, you’d love even more!!” but (1) you have no way of measuring the strength of someone else’s love, so you’re just kind of pulling that claim out of thin air, and (2) it’s awfully obnoxious to assume that you’re capable of some kind of “greater” love just because you have different opinions than someone else, and (3) even if it were true, it wouldn’t change the fact that atheists can and do love and can live a life of love and joy, regardless of what claims they accept.
So again, the answer to “What if you’re wrong?” is – “well, I’d live the same life I do now, a happy life filled with love. You say that I’d love even more if I believe something different. Well, maybe you’re right, but I don’t agree with you, and I don’t see any reason to think that what you’re saying is true, so I guess I’ll never know. Bye.”