It is very rare for an 18 year old to have complete coverage, so try not to focus on the areas that are still developing. Rather look at the big picture. Is it symmetrical? Yes. Are there gaping holes? No...in other words, it's looks quite good on you you should just enjoy what you have now! In time, those areas will fill in, but don't expect it in the short term.

Patience shall be rewarded!

New beard growers: Check out the Rules of Beard Acquisition.
To upload and post pictures, here is a tutorial.
Do you believe in these Common Beard Myths?