The best way to finish a bimini is with a pull through loop, this is the same as you are already doing but with no half hitch. The problem with having the half is it stops the pull through coming up tight, ie its supposed to pull back up into the bimini.
The easiest way to finish a bimini is to just use about a dozen opposing half hitches,make sure you pull them all up tight.
The best and easiest way in a rocking boat is to not do it...Take a spare spool!
I have been trialing a new knot for connecting to twisted leaders that deletes the bimini from the whole system. Hasn't failed me yet , very small ,no double, easy to tie in any situation.