Getting into exercising

I have started to see myself burning calories.  The new message I wrote on my card is "I am a fat burning machine".  This has become my mantra, the thing I say over and over again to myself.  Since I started meditating on the saying I have noticed a lot of negative thinking that goes on inside my head. I have learned to quickly change my thinking to "I am a fat burning machine" and all the negative thinking goes away and a little happy feeling comes over me.   I started imagining myself exercising and it finally clicked.  I was laying in my bed one morning and pretended to ride my stationary bike and about two weeks later I started riding my bike for just 10 minutes and that 10 minutes has changed to 15 then 20 and now I can do 20 minutes rest and do 10 more. For me this is really big.  Wow!