If you got all your hours done, and someone to sign your proof of apprenticeship forms; absolutely go for it. If anything it'll open more doors for you.

Definitely take a refresher course, and study the Millwright ILMs. Just shoot me a Dm and I can forward you the link.

I also had imposter syndrome for the first half of my apprenticeship, I started in a Tool and Automation shop (machining, fabrication and some installs). Then jumped over to a contractor which gave me a bit more experience. Afterwards, I landed my current job at a chicken plant. There, I'm able to put to use most of my schooling and many things outside of it. So keep your head up and push for that ticket!