It's a very neat game concept with a lot of potential. The style and gameplay reminds me a bit of any of the simulator games, like PC building Simulator, but instead of building PCs, you're tying people up.
My review for this is that, with the current build, it's very clunky. Like, I tried to exit to the menu, it will not exit, it gets stuck on the loading screen. Aside from that, while I love the gimmick of drawing knots to show the tying up process, I think 15 is a bit too much to draw, I think the sweet spot would be around 7 to 8 ties. If you want to make it less, make the knots more intricate.
If there's anything that needs to be added, it would be a mode where you can test out what materials/ties you can do on a blank slate. As well as, the ability to see the model of the character being tied on all sides.
In terms of items used for tying, and how someone is tied up(positions of being tied up) I think that'll be a later addition. Which is up to the creator of the game themselves.
Overall, I think the game has potential and would be a good time waster.
P.S, I do love how you emphasize the safety of the person being tied up.