Q: What should I do if I submitted to another journal after misunderstanding the 'Revise and submit' decision by the original journal?

This is unfortunate, and I can understand if you feel a bit annoyed – by your misunderstanding of the status, by the second decision of ‘Revise and submit,’ and by having gotten into a problematic situation with both journals. However, do not worry – this can be handled. :-)

Firstly, you have already done the right thing by writing to the first journal to withdraw. What may have been better is to have explained the situation to them and then asked them to advise on how to proceed. This is especially because the first journal seems to have been your original choice. You could still do this, but for now, you should wait for them to get back on your withdrawal mail.

What you need to also do is to write to the second journal informing them of the situation. Here, you have the opportunity to seek advise from them. Based on what they suggest and also on what the first journal suggests, you can decide how to proceed.

Of course, you may also need to continue working on the revision request by the second journal – unless the second journal suggests you withdraw from them.

In a worst case, you may have to withdraw from both journals and submit to a third journal. That may sound even more annoying, but unfortunately, that may be necessary.

Again, the situation is unfortunate, especially given that it was a misunderstanding, and a genuine one. Hopefully, both journals will understand your situation, and you will be able to arrive at a satisfactory resolution.

As a final note, ensure you follow all the actions for withdrawal as suggested in this query by another researcher: What can I do if the editor does not confirm my withdrawal request?

Based on the situation you have described, you may also find it worthwhile to invest in this resource: A guide to understanding journal statuses [Handbook]

Hope that helps. All the best for all the next steps!