Training for sprints / short races How do I train / fool my body to go anaerobic for intervals?

I entered my first cyclocross race a couple weeks ago and have since been training on the course.  

What I found during the race and my training is I get gassed (can not even talk) on the first lap but after that I settle in and breathing is just heavy. 
But my times lap to lap do not change. 
Day to day I will get different lap times as I am trying out different set ups and the ground may be softer or harder but in a session in the 6 laps the times will be within 3 seconds. 

I am in a health study and take a treadmill every 6 months.  At a certain level the Dr will tell me this is your target training level and it is not very hard.  I have trained my body for that level and it is kind of stuck.  They did not tell me I could not train at a higher level - just train at least 50 minutes at that level of higher.  Dr told me he would rather I went with perceived exertion rather than heart rate. 

Also I live in a large flat city where I don't have road routes that I can readily do interval type training.  We have some bike paths but with turns and other riders it is just not safe to ride full out.

At the gym in a kick boxing class of other interval type training I do gas out. 
On the bike I seem to have some type of governor.

Lets just start with the last lap. 
How do I train / fool my body to go anaerobic on the last lap?
Anaerobic training is without oxygen, so you are using the lactic acid energy system. This means to be going above 80% of your Max Heart Rate MHR (or above 8 on perceived exertion table (can barely talk)). If you are solely in the anaerobic region, you can only go for 2 mins (ish) at that intensity. This means you will need to be in between regions, so you are using both major energy systems (with and without oxygen) to last 7-8 mins (of last lap).

If you are to use perceived exertion rather than heart rate you basically have to go hard out the whole time. You have said that you get gassed on the first lap i.e. perceived exertion is high, this could be due to an insufficient warm-up as Slovakok mentioned. This is where heart rate is helpful, it is accurate and tells you exactly what you are doing. Other wise, you could do one lap and get gassed then once you settle in start to go a bit harder to match the perceived exertion of the first lap.

A good way to get into the anaerobic zone is to do interval training, maybe once a week you could do three laps with a rest in between each lap, go as hard as you can for one lap, then rest until your heart rate feels normal again, or you think you can repeat the effort (might be 5-10 mins rest), then next lap go hard again, then rest a similar time... The next week try to rest for less time and continue decreasing rest until you can do 2 laps at that intensity or something like that. Other things to try are hill sprints, plyometrics, time trials, and just training in the anaerobic zone as much as possible, also training's work differently for different people, so you need to find something which works for you.

Basically you should set some goals for where you want to be in x weeks, and remember that  to be able to race at anaerobic level you must train there as well. So just go hard or go home on that final lap i guess (in both training and racing).