That is OK to miss a meeting. It is bound to happen once (or a few times) per year. All the required and/or elective adventures can be completed at home! Contact your den leader and they will be able to provide you with the adventure the den was working on during the meeting so that you can complete it at home. Either a parent/guardian can sign off on your scout completing the work or you can take the work to your den leader so that they can sign off on the work and mark your scout as completing the requirement.