Hi Mitch. Welcome to the beard board. 3 weeks is a little early to say whether the sides will thicken up though I'd agree at the moment that they are your weaker areas. Given some time though they may well sprout nicely! As for the moustache you have options! Many guys on here will maintain a longer lip weasel but train it to grow out to the sides. You can use 'tache wax to do this or you can simply use your thumb and forefinger to push the hairs sideways several times a day until they train themselves. Of course if you are looking for a shorter beard style then you can keep your moustache trimmed at just above your lip line.
If nothing else you could sport a great riker style beard fairly quickly. Happy bearding. Wolf