Instead of I should have been tougher and raced better, it would be more helpful to say I want to race better than I did and will work towards that goal for my next race. It's a minor difference, but should is judgmental. Should sets me up for feeling like a failure. Identifying what I want, on the other hand, formulates a goal and provides a foundation to make improvements. Basically, the difference between should and want is the difference between disappointment and hope.
So yes. I want to do better. I will do better. It will take time to improve my fitness and it may take longer than I want it to given what's going on with the rest of my life. It will take time to get those racing sensibilities back and improve upon them. So, as always the answer is to keep plugging along, but leave all those shoulds behind.