You can probably expect a slightly lighter, lower alcohol version of the beer you intended to brew. I suspect you still may end up with a decent beer though as your OG isn't low enough to really worry.
For your next batch, I'd suggest you measure wort volume well before flameout though. If you continued to boil to reduce volume rather than stopping at the end of your normal boil time, you'd end up with increased bitterness due to boiling your hops longer. You really want to make that adjustment at the start of your boil, before adding hops, not at the end. Once you understand your system boil off rate, you'll know exactly how much wort to start with to hit your final volume dead on.
The Homebrew Nerd
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