No worries fleas. Contamination at that stage is usually rare for mainly two reasons. One is that you now have a preservative, namely alcohol. Secondly, the things that tend to prey on your wort are usually a concern pre-fermentation when they have access to fresh sugary wort. Once the process is complete there is less chance of anything happening that would ruin you, but they do still exist so caution is always in order but that doesn't mean you should worry. What it does mean is to make sure you sanitize what comes in contact with your product and to mess with it as infrequently as possibly, only taking readings/etc when necessary.
Fwiw, once you become more familiar with the process (and specific recipes) you should be able to not interfere in the interim period but rather let the wort fully ferment before taking a reading. Racking is always a good time to take one as you have, but just wait until all activity stops and record the FG when you are ready to bottle.