My first ever work experience was establishing whether patients sending stool samples by post could be feasible. After playing with various samples and the folding card containers, luckily inside a fume hood, I concluded it wasn't...
Just sit slightly sideways on the loo and scoop up some that sticks to the side. Or poo as normal and reach in and scoop up a spoonful - doesn't matter if it's a bit soggy, unless they've told you otherwise? A teaspoonful is more than enough!
My sister did this not long ago and have asked her for you - she said you have to poo into a container, something you can obviously dispose of and then use your spatula to get a small amount (roughly 1/2 a container full, screw on the lid VERY tighyly and flush the remains down the toilet and bin the container.
If you're handing it in tomorrow, maybe try your best to wait till morning to do it so you're not in your house thinking 'oh my word there is a container of poo in my house'.