"Has the engine been damaged?" That depends on how your
exhaust is set up, and whether you pumped long enough to fill the waterlift and flood the engine. If you take out the spark plugs and run a cotton swab around in the cylinders, and it comes up with just normal oil/fuel and no water--you're probably OK. If there's any evidence of water in the cylinders, then you may have done damage. Also check the oil, make sure there is no milky foam indicating water got into it.
If you are feeling ambitious or cautious, you can remove the cylinder head to check for valve damage. Otherwise? I'd suggest draining the muffler (to make sure it isn't still too full) and then cranking the engine over (plugs out, water shut) to see if it sounds normal. If there are any odd noises, might be time to pull the head. If it sounds normal...then put the plugs back in and fire it up, gently, to see if it runs OK.
Without tearing it down, there's no definitive way I know of to make sure there is no damage. But if it runs OK, sounds OK, it probably is OK.
This is assuming it was OK to start with before you did the compression test. Was there a reason you were checking that?