gravity sample

Hello everyone
I just took a gravity sample from my batch..It was 1077 now its 1020..i know i still have some time,seeing its a pretty big beer and the yeast has not dropped yet..Can i just put some foil over this sample and use it to moniter my attenuation? so i do not have to take another sample out of the fermenter? I am assuming that it will continue to ferment inside the test tube..The sample tastes great so i dont wanna risk infection cause this batch seems to be going perfect..I had wishful thinking going into this,hoping i can clove a duvel and to my surprise the sample taste like a "green" duval and im super stoked..what do you all thing about the test sample? keep it or toss it?
thanks

You can do this, but fermentation conditions in the tube are very different from the carboy and will only give you an approximation.

With 1.077 down to 1.020 you're at 7.5% alcohol, so your risk of infection is pretty low. As long as you're using standard sanitation practices you have nothing to worry about. That said, just leave it for a while. You're already at 74% attentuation which is great. Time is your friend. Don't toss the sample - drink it!

Drink the sample, and take another in a couple of weeks. The sample will not represent what is going on in the beer. If you expose it to excess oxygen, it's probably going to start tasting awful, and ferment lower than the actual brew.