Tying off the knot

Does anyone else ever have issues when you’re tying off you’re not at the end of the row and your looping the string three times through the center of the loop and it ties a knot before you can actually pull it tight? I hope that makes sense! But basically there’s still slack in the string that could go tighter. I tried the cotton string and nylon and had it happen with both. It also happens when I’m starting the row and doing my first knot....I wish I had a finger in there to hold the knot down while I do the second knot. 😂