Need for speed most wanted Vita. What am I missing? Please help!

Hello. I am new to the NFS world and I just bought most wanted for the PS Vita. I feel like this game is so incredibly difficult that I must be missing something. 
For each car that I find, I need to complete races specific for that car to unlock upgrades for that car. Typically when finding a new car there is one race that is classified as "Easy". I seem to do ok with this race which usually unlocks nitro and off road tires. After this is where I stall out. 
The "medium" races seem to be incredibly difficult. I can drive what seems like flawlessly though never even come close to winning the race. Like my car is just not good enough to compete, but the only way to upgrade the car is through these races that I can not seem to do squat in. 
I have reached enough speed points to challenge the #9 MW car but I cant even come close to defeating the #10 car. 
What am I doing wrong? I really want to love this game but I feel like I want to throw in the towel on it. 
Any help is greatly appreciated! Thanks everyone!