u/Fickle-Attitude787

Hello all, I’m trying to add a window screen to my bedroom window and am having trouble. I initially thought I would measure from inside the window frame where the window frame will set end to end, but as you can see in doing so based on the photo there is no way that frame will get past that little lip. Am i supposed to measure from the left where the frame will set against to the lip or to inside that deepest part like shown. Would the same thing apply for height given that there may also be that lip at the top ?