The wheel fits in the drop outs now? And you want to add spacers? Then what, just shove it in there?

At any rate, don't space the hub on the axle such that the rim in not centered when the wheel is mounted. That's a completely bootleg shortcut and a terrible way to get started. If you use a spacer, re-dish the wheel - which is also bootleg on a flip flop.

Someone slap me. What am I talking about? You don't want to replace the cranks or bottom bracket to make this proper. So it's bootleg.

Yeah, add a spacer. Then check back when you are ready to do fix the non-issue correctly.