I agree with Shazzie, it’s always a good idea to take a couple of painkillers with your injection just in case. I found ibuprofen helped me the most. Not sure what dose you are on but I started on 22mcg so I did get side effects straightaway, a bit achy and headachy like when you’re recovering from flu.
Have a fab time at Ascot. Take some painkillers with you and then forget about the MS for a day. The best medicine ever is to see friends and do normal stuff. I guarantee that this will lift your mood better than anything else - except a glass of bubbly perhaps?! 
Tracey x