Welcome Lizzy Bee to TE. It sounds to me like you are on the right track if you don't burn yourself out. Remember that this is supposed to be fun.
If you are already riding 45 miles and continue training the way you are, you should have no problem doing a century in August. You will also find that your speed will increase with your mileage, strength and endurance. One of the things I enjoy so about cycling is that you can see improvement weekly which makes you want to push harder.
I did my first century (in was actually 109 mi) in a little over 7 hours with a 14.9 average but there are other things to consider besides time and speed. I wasn't prepared for the fatigue and mental stamina it took to complete 100 miles. Somewhere around 80 miles I almost had a meltdown and started cramping. I had to stop every 5 miles to keep my quads from cramping and the biggest hills were in the last 10 miles. I did a lot of self-talk to push through it and finish.
Are you doing this solo or do you have a partner to train with you? I would suggest you have someone experienced riding with you to help you through the last half. I would also suggest you do this on a charity ride where you have support and you don't have to plan rest and food stops.
Good luck and keep us posted on your progress! It's an accomplishment to be proud of.
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"We don't stop playing because we grow old; we grow old because we stop playing." George Bernard Shaw
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