Offset inwards - new curves are too short

Hi all, trying to offset a curve inwards but whatever I do the generated curves are too short and there are sections where the new curves cross over. Looks like they’ve been offset from each of the constituent lines of the curve I’m offsetting. Hopefully the screenshot below will explain that better than I can!

Anyone know how I can either join these together or offset this correctly? Thanks!

Urban proposal (22.0 KB) Urban Proposal v8_forum.3dm (671.3 KB)