One thing you absolutely must remember is that any form of tampering on common seal impressions is not allowed, even when it’s done with good intentions. Don’t try to fill in the rest of the parts by impressing on the same spot or trying to fill it in with ink.
What you can do is to make a second new impression near the first with your common seal and make sure this one is clear this time round. Don’t try to overlay it with the first- any place near would be more appropriate as long as it will not be covering or interfering with any other text/image in your document. Ensure that this impression can be seen clearly and photocopied- if you can achieve that, then it will be fine.
In the event that there is no space left on the document, you can attach a second but complete piece of document with a complete impression of your common seal. Remember to cross out the incomplete impression and divert people’s attention to the complete one by including a clear call to action like “See Attached” or something similar.
Another recommendation is always that prevention and precaution is better than rectifying it. So take a little time and patience to do a test impression first before you perform the actual impression with your common seal. Make sure to shred the rough piece of paper with your common seal impression so no one can duplicate it!