Okay, first and foremost, you're track is too wide if it's a full size car/bike cirucit, this is more like a kart circuit with the width and length.
Have a look at other people's circuits for ideas on scale regarding track width and length.
I usually tend to plan it in my head before hand, thinking about lenght, and the purposes of the circuit, if it's a fully fledged international venue, or just a smaller, national type circuit.
I like the general shape of your circuit, and with some tweaks, it could be pretty good