please god how do i beat the last c level i need this
There are only a few sensible options for where the 3-long piece can go. When you find the right one, at least a couple other pieces might fall into place when you think about the possibilities for a nearby endpoint. There are four L-shaped pieces, so you'll also need to think about all the places you can put them while still leaving room for all the other branching paths that are going to be necessary.
If you made it to this level without needing help, I'm confident you can get this one too. There's a solution in one of the videos below but I don't think you need it, if you feel like giving up then maybe come back later and give it a fresh try.