When I had about the same number of hours as you I was offered a check out in a Mooney. I turned it down for the same reasons as you offer - and I regret it to this day. At the time I'd only flown C150/C172/PA28 aircraft and thought it too big a step with so few hours.
25 years later I now have 28 types in my book ranging from the lovely DH82 to a PA31 but I never got the chance to fly a Mooney again..
Yes, the aircraft is more complex, it goes faster and your thinking has to gear up to this. It's your instructor who will tell you if you are pushing beyond your own limitations - you can't guess this beforehand.
Go for it.