Newly motivated

Hey there,

So I've been on and off this "losing weight" journey for ages now. Here's a little about me:
I'm 23, 5'5, about 250 lbs (oops, I know) and I recently got a wake up call from my doctor that I am pre diabetic. I have a gym membership and when I don't go before/after work, I look up some workout videos on YouTube. I recently started doing this and I'm feeling a lot better but again, it's on and off. I want it to become a permanent lifestyle change so I'm slowly working at it.
My fat is horribly distributed in my opinion, a lower abdomen fat (fanny pack fat I think they call it). So my questions are, what do you all recommend as a good exercise routine at the gym? I usually have about an hour at the gym before I go into the office or an hour after.
What I normally do is:
- 20 minutes cardio (10 min stair master and 10 min elliptical)
- The rest is divided on legs and arm machines.
I don't know if this is enough or if it will be effective. I've also been trying to eat healthier!
Would really appreciate any insight. Thanks in advance!