LP,
You haven't told us the type, but lots of things might go wrong even with an apparently simple manoeuvre. Even experienced aerobatics pilots have things go differently from how they expect from time to time. Their experience and training are then what they draw on to get out of those situations.
What might have gone wrong? Much depends on the type. But, for example, you might have found something heavy drifting up from the floor or the luggage compartment and whacking you in the head, or you might have gone slightly negative with a carb-fed engine and had it stop on you, or you might have got disorientated upside down and slackened off the aileron (quite common I believe among people trying their first roll) and gone into a high speed inverted dive, or you might not have got the nose up high enough to start with, with the same result. Fortunately none of those things happened.
I don't have any real insight into how you went about it, but from what you wrote it comes across as very much a spur-of-the-moment decision, no real preparation beforehand. Spontaneity is not a terrific idea when you're starting aerobatics, a very methodical and disciplined approach makes it much easier to cope and learn in safety. While a few people have successfully taught themselves aerobatics (though I don't recommend it) I'd suggest those who have survived are those who have gone about it with great caution and foresight in other respects.
flying something aerobatic (+6/-4G i think)
It would be safer to know the G limits than to think you know them. Had you read what the POH has to say about aerobatics in that type? And is that G rating valid at the part of the loading envelope that you were actually operating at? What fuel did you have in what tanks? You used full aileron, and at 100kts that's probably OK depending on type, but do you know the max speed for full aileron application? Do you know the way that aileron deflection generally reduces the load-bearing capacity of the wing, so the more roll, the less G you should pull? Did you know for a fact there was nothing in the luggage compartment? Had you done a loose articles check? Were you in suitable airspace, and what kind of lookout did you do? Did you do the HASELL (or similar) checks that you would do before stalling, spinning etc?
I think you'd find a course of dual instruction, and the accompanying groundschool, both fun and illuminating, and it should certainly include the importance of those questions.