Swivel rod holder install question

[CHANCE1234]

So I bought a swivel rod holder for the bow of my 20 for the super nice days I can chase tuna on the cape. The entire cap of my 20 is solid glass except for the bow area that is coosa or plywood (which ever is factory). I installed the rod holder with the supplied backing plate and also added a 12"X12" 3/8 piece of starboard for extra strength. When I put the rod in the holder and pulled on the line there is obvious flex in that area still. Short of pulling off the cap and reinforcing that area what are my options to strengthen that area. If I have to pull the cap off ill just return the rod holder. Thanks for any suggestions.