The key to improving your health and fitness relies on 2 aspects. Firstly, yes you need to get more active and work in the gym, in the pool, with a sports team or something similar. Doing this will get that metabolism up higher, teach you how to move, look after your body and generally get your confidence going. The second thing is all about what you do in between those workout sessions.
On that point, going to the gym for 3 hours a week isn't a huge amount of time to focus on your health and fitness. There's 168 hours in the week so spending 3 of them working on it is just under 2% of the time available. Yes, that 2% may be some of the most valuable but you can't ignore the other 98% if you want to be successful. My advice for you today is to work on that 98% to get your health and fitness improvements.
It's the little things that make the difference here. I'm not trying to tell you to spend 3 hours a day in the gym, instead I'm advising you to think about your movement throughout the day. Instead of spending hours on end sat down, whether that's at work or at home, get up and move every half an hour. Get up and do 10 squats every half an hour when you're sat down. When you go up and down stairs do it twice (up, down, up or down, up, down). When watching TV do a few lunges every so often. Instead of driving places, walk or cycle. What we're trying to do is substitute sedentary periods with periods of gentle, low level exercise.
An example that I do myself every day is utilising the time between clients. If I have a gap between clients on any day and I'm in the gym then 9 times out of 10 I'll go for a walk instead of just sitting down waiting. I make a point of walking slowly and steadily so as not to get too tired or out of breath (which means it's sustainable over longer periods of time). The difference this small change makes is fantastic. By doing this alone I'm standing and moving for an extra half an hour a day, which adds up to over 3 hours a week of extra movement. That's another 2%. Get a handful of these different ideas going in your life and before you know it you'll be tripling / quadrupling the amount of time you spend moving and drastically reducing the amount of time you are sedentary.
Want to know a little more about why this is good?
Just do an internet search for 'effects of sedentary lifestyle on health' and you'll find lots of information and many, many scientific studies.
What should you do with this info?
Well my advice would be to think about your lifestyle and the times you're particularly sedentary at the moment. Once you've pinpointed an area you think you can improve then think about what you can do to get moving more. Remember not to make it too hard or seem like too much effort to do. Next you just need to get in the habit of doing it. Simple as that!