I’m so sorry that you have this rare sarcoma.  My sarcoma is different to yours but I totally relate to your feelings of being in limbo.  That was my experience in having to go through a series of tests with what felt like very large gaps in between each to get the diagnosis and then had to wait about a month before starting radiotherapy and then 6 weeks after that I had surgery.  Are you being treated at a specialist sarcoma centre?  You should be.  Unfortunately even the common sarcomas are extremely rare but the network the different centres have ought to help and if you are not happy you can always request a second opinion.  I think you will find yourself considered rare and interesting so you will get excellent and prompt attention.   

I do very much hope all goes well for you.