I'm glad this post was resteemed by helpiecake, I probably wouldn't have seen it otherwise.
It sounds like this turned out to be a good first project! Subwoofers can be a bit tricky to build, you never know quite how they're going to react in the box, even when you build it to "optimum" size, because the speaker parameters aren't always what they're advertised to be.
P.S. I didn't realize this is only your second post on the blockchain, you should consider posting more often.
I recently put together a set of horn tweeters for my sound system due to a lack of upper frequency response. I made temporary boxes for them until I can work outside to make better boxes. I wrote a couple of posts about them, in case you're interested in checking them out.
I think I need to get one of those DATS speaker measuring device for building woofer cabinets for a couple of 12 inch speakers that I have no boxes for right now.