How does an inexperienced pilot handle G-Forces?
The  G-limit for the Extra 300 (the parent airplane to the 330):


  The Extra 300 is stressed for ±10 G with one person on board and ±8 G with two


So it is certainly possible from an airplane perspective that you pulled that many Gs - in an aerobatic airplane, it's not unheard of to pull 1G less than the aircraft limit (usually there is a large margin of safety built into that number before a catastrophic structural failure).

Now did you pull 7Gs? As others have noted, 7Gs for 10-20 seconds seems very unlikely. But it is not out of the question your peak instantaneous G load was 7.

From a human factor standpoint, G-suits typically don't increase the max G-load, but rather increase the sustained G-load and the time period it can be held for. G-suits do very little to actually decrease blood flow (pooling in the legs) - they primarily serve as a reminder to the pilot to perform an AGSM. 


  A g-suit does not so much increase the g-threshold, but makes it possible to sustain high g longer without excessive physical fatigue. The resting g-tolerance of a typical person is anywhere from 3-5 g depending on the person. A g-suit will typically add 1 g of tolerance to that limit.


Now there are a vast array of factors affecting this resting G-tolerance. I flew  a military high-performance trainer, and my resting G-tolerance was around 3, or the lower end of the spectrum. One of the other pilots I knew had a resting G-tolerance of about 7.5. The primary difference is blood pressure. I am 5'10" and only 145 pounds, with a resting blood pressure of about 90/60-100/70. He was 6'0" and about 215 pounds, with a much higher blood pressure. Tall, skinny, nonsmoking runners have actually the worst resting G-tolerance while short, stocky, sedentary or heavily muscled smokers have much higher tolerance. Other factors, such as how hydrated and rested you are and how much stress you are feeling, can vary vastly your daily G-tolerance. 

All of those numbers I just listed do not take into account the pilot performing an AGSM (Anti-G Straining Maneuver). This can add several Gs to the pilot's tolerance, and is one of the biggest things taught in physiological training for high-G maneuvers.

So TL; DR: could you have pulled 7Gs without prior exposure? It is possible, depending on varying personal factors and body type, but it is not likely. However, with a little training, 7Gs is perfectly attainable.