I'd suggest taking some pictures and showing them to a local loft. They may be able to recut the leech of your sail a bit so it fits the shorter boom properly, and that would give you a little less sail area, possibly a slightly different balance, but a neatly finished look to everything.
If the aft end of the boom is simply sliced off and capped with a plate, and you don't mind doing a lot of scrounging around, you may be able to get a section (ask the spar maker) that fits snugly inside it, so you can extend the boom another six inches or so if that's all it needs. Considering the size of the boat...a good woodworker or a patient sailor could probably take a piece of 4x4 deck post and trim it down to make a good extension as well. Given the size of the boat, and the minimal length you should need, strength is probably not an issue. For that matter, you might be able to take the boom into a local metal shop and have them fab up an extension. Again, take some pictures (end plate off) and ask around.
Or you could always ignore it for now, and try to shop around for a slightly longer used spar, but that could take a while to show up even if you've got a good consignment or breaker shop around.
Visiting the sailmaker probably is going to be the quickest & least painful way to go.