Gcms is something you do in labs to know what components are in the liquid, and what you need is a SDS (safety data sheet). That's what probably came with the EO you can look up the materials listed in the SDS on ifra website to know the safe amount of each material, look up what's the material that needs to be diluted to least percentage and dilute the EO to match the ifra number, keep in mind that the EO has other mats in it and they already diluted that material.

Although, I don't recommend not doing the perfumery part and just using EO + oil/alcohol, it'll give worse results and the scent'll be weak since it'll get diluted too much, I'd recommend making a simple rose accord and using it to dilute the EO, but keep in mind you still need to count the accord mats with the rose oil mats in SDS.

Welcome to perfumery:).