You can affix a second seal near, but not over, the original seal. If the space is tight you can turn the seal sideways, particularly if it is a real property document and a seal is mandatory.
If there is no room to affix a second seal, you can affix a separate document with the proper jurat and seal but remember to cross out the original with a single line and note "see attached document" to the original document. Tampering with the original seal in any way is strictly not allowed.
A good first step before affixing seal is to do a practice stamp to make sure it is in proper orientation and is sufficiently inked.