This is totally normal as a repair to a supraspinatus tendon can take many months to become more pain free. The 90 degree range is likely to be where the work that has been done comes into contact with other soft tissue structures. You can benefit from gentle soft tissue massage to desensitize the area being careful not to over do it. In my experience you should not push range of motion but let it return as the tissue swelling/thickening resolves. Don't be surprised if this takes up to 12 months.

You really should be working with a physiotherapist during your rehabilitation of this repair to monitor and plan your home exercises so that they are a steady, progressive return to full normal function.