If your fiber seems a little loose when sliding it into the lens you can first take a pliers and slightly clamp the center area of the fiber where it would be positioned in the lens this will give the fiber a slight oval effect thus snuging up fit so its not flopping around loose I would take a little heat and ball the ends some just a little so fiber will draw enough light and you have a nice aiming dot.
Some have used wax to hold their pin, I'm not a fan of this do to the mess that can end up on a lens that may show up right at the fiber optic dot area - your aiming area when looking thru and aiming.
Just something we have done in the past when setting these up I hope this helps
A side note for outdoor we have went away from center drilled lens and have either used sticker dots on a lens or a normal lens used with a fiber optic wrap with a up post allowing a person to take the lens out of a scope but yet still have the fiber optic for aiming with less magnification do to the course or weather conditions
Good Luck and theres never a dumb question here!