Yipes! i had great success with my son by continuing our nightly routine of "bath, brush, book then BED". i stay in his room just long enough to read, say the prayer with him & allow him to speak about any last thoughts before he goes to sleep.
i would never recommnend locking your son in... that doesn't teach him how to control himself. which is what i think going to bed on one's own is a demonstration of... self reliance & independence.
My son has been sleeping in his toddler bed since he was one... He never liked the crib. He is three now. At first, we really tried everything to get him to sleep in his own bed without me rocking him to sleep, (which i did for the first two & ½ years of his life) until we just went for it & told him what was what. We transitioned him to his new arrangement by making it a “big boy” event & i bought him a special “big boy” pillow case for kids who go to sleep on their own- in their own bed. i still sit and read to him before bed in the same rocking chair he would fall asleep each night.
Remember you are the adult. You are ultimately in charge. i think we forget this or get too tired for a struggle so we give in... it’s important to stay the path.
i just stayed consistent with the routine, preparing my son each step, especially before reading, that he would be getting into his own bed & staying there to sleep. At first, our son would come out & talk with us or ask for things (water) & we would just remain consistent verbally by telling him how it is and with action by walking him back to his room without negotiation.
Every time & again, i have to still calmly put him back to bed, remind him i am just in the living room working on something & that he needs to stay in bed. He usually goes right to sleep or sings to himself in bed on the first try, but every now & then there are those nights where i have to walk him back to his room & tuck him back in.
Keep trying. Your son will get the hang of it! (and so will you ;) hope any of this long winded response helps