Wardegul (Sept/Dec 2017, amended) using interest rates instead of future prices

Hi. I am working the Interest rate futures (IRF) section of the past exam question ” Wardegul (Sept/Dec 2017, amended) from the BPP revision kit, but, instead on working the answer out using the future prices, I am using the interest rates. Upon completing my answer, I notice that it is different from the model answer, my net return is 963,500 and effective annual rate is 4.92%, whereas the kit has net return of 515,250 and effective annual rate of 4.58%. I’m not sure where I’m going wrong, can you please assist me?