If you had gone to a real plumbing supply store, you could have picked up the proper coupler and not ended up with some kludge that, while it may work, doesn't pass code.
It can be quite dangerous cutting a section of CI pipe out of a run. Depending on how things are assembled above it, that section which could weigh hundreds of pounds, is now hanging there. The PVC is NOT designed to hold that weight. If you don't have any, you really should pick up and add in some proper clamps to hold that section so it doesn't gradually creep down as it slowly deforms the lead in the joints above.