Do not feel bad, because in racing how deep your pockets has a lot to do with who ever is doing the best times. I've learned this the hard way
In Sebring, people say below 2:30 is a reputable time. I was doing 2:24.8 the last time I was there, my car only had Toyo RA1 (-2 seconds per lap) and solid rose joints (-1 to -1.5 seconds per lap), so I was running good times. Still I was getting sh!t from people.
I even hired a pro driver to help me out, and he said I should be racing in amateur division. Which is a good sign.
It is possible to get close to record times, but at what cost? When I did a cost analysis I realized it cost me about $1k per track day with the GT3 not counting the wear and replacement on the engine and the transmission. Hence the reason for me to quit and sell the car.
There are two factors to becoming a faster driver:
-Natural, God given talent
The more talent you have, the quicker your lap times will drop. More seat time will allow you to become more comfortable with your car, approach it's limits, learn where the car understeers and oversteers. We all make mistakes, go off the track, spin, don't get discouraged; but learn from them! Listen to your instructors, most of them have more experience and know more.
I have done 40 DE days, hired a coach for helping me lower my lap times who at the end of the day said I had talent and suggested I get into amateur racing. I wish I could but I don't have the budget
Anyways, there are guys that I know with deeper pockets, better cars, more experience and more cheater parts who are running better times. There's nothing I can do about that. It's a bottomless pit.
Because of the length of the track, I'd say your tires, suspension and brakes give you an advantage of more or less about 4 secs over a stock car (-1 to -1.5 secs for tires, -2 secs for suspension, -1 secs for the brakes). Keep that in mind and aim higher