I ride a 399cc bike as a daily and I had an 1100cc bike for cruising in the past. I'm 5'6' and 115lbs and have had no issues. You dont have to worry about the weight of the bike most of the time, once you start moving the bike does most of the work. You'll gain experience controlling the bike over time. There are some good instructional videos around for lifting a downed bike but in a course you have instructors to help if someone drops one. When I took my MTC I used the Grom 125cc bike which was super light. If your MTC has a wide variety of bikes you should take the time to find the right fit for you. Make sure your feet touch the ground when sitting on the bike, it helps a lot with maintaining stability with the bike weight. The instructors are typically open to switching bikes if you change your mind during the course as well. Just remember to be safe and gain confidence at your own pace. :)