Here's the thing...

It is true that riding with your seat lower than the optimal height can do a few things. It overworks your quads and glutes. It can give your knees a bit of trouble. It is not as efficient.

BUT....

If you don't ride at all because you are not confident to ride at the optimal height, then that is a big shame. So if it is not giving your knees, quads, glutes etc any trouble, and you don't care if you are not quite as efficient as you could be, then I reckon you should ride at whatever height you feel comfortable with for now!

I'm sure in time you will gain confidence and speed and distance and you will want to be in a more efficient position (and aches and pains may even dictate it to you) and then the seat can go up a bit more. Do what feels right for you.