Not yet, you need to do more miles...but you can give it a try if you ride more miles, eat and drink enough and have a bail out plan. Going from 20 miles to 100 is an enormous leap, you just don't realize how bad you can feel until you bonk with 20 miles to go. I strongly recommend that you increase your mileage and do a few 50 mile days and a couple of 70 or 80 mile days. I'd take a bit longer than a month to do this so you don't get too tired or injure yourself......good luck.
That's good advice. I pretty much figured I'd be told what you've written, but I also hoped someone would say...sure, 20 miles to 100 miles is a pretty logical step. Do you think 1 month is enough to train from 20 miles to 100?