Half of wort boiled away - newbie

This is my first attempt and I’m using the 1-gallon starter kit with Caribou Slobber. By the time I finished the 45 min boil and cooled the wort for transfer, I ended up with only about half a gallon. Did I do something wrong, or is there something else I could have/should have done?

You can top it off by adding distilled h2o. Just add water till you get a full gallon. All of the fementables are in there, so if you top it off, it will be at the specified gravity. If you leave it, it will be at a higher gravity.
Welcome aboard!!! Learn a little every batch, relax, and enjoy!!!

I’ve brewed about 35 batches, and I’m still learning something every batch. This forum is great for learning, use it well.

You may have had to hard of a boil going. A boil doesn’t need to look like a volcano, just enough heat to keep part of the wort surface rolling. Kettle dimensions have an effect on the rate of boil off. A large diameter kettle will evaporate liquid faster than one of lesser diameter.
The boil can also be done with a lid partially on to reduce the amount of heat needed to maintain the boil. I wipe the condensate from the underside of the lid, when it begins to form large droplets, just in case precursors to DMS may be forming instead of leaving the kettle in the steam.

I actually just brewed my first ever 1 gallon starter kit last night, and it may be a bit of a mixed blessing that you ended up with less than expected. I ended up with a little less than a gallon and it’s made quite the bubbling mess so far - it’s finally starting to cool down and stop bubbling free of its lock after 28 hours. Thankfully all the seasoned brewers around here tell me it’ll be fine - just to consider a larger container next time.

Funny thing though, two newbies with two different results - me wanting less, you wanting more. Enjoy! The trial and error has been fun so far.