It seems to me you have a bigger problem than rudimentary css skills (although thats a problem): lack of business acumen. The dentist obviously wont have a clue what hes paying for - you could either try to rip him off, or deal fairly and look to build a longer commercial relationship (which can be more lucrative than hit & run).
Im not just talking about price, either, but value as others have written above.
However, you dont seem to know what you can bring to the table either - so I feel sorry for the guy. Caveat emptor, however.
You appear to know little about sales (probably the single most important skill in life, let alone business) - i mean, to establish the offer, handle negotiation, set & manage expectations, contracts etc etc
There's only one way to learn that: by doing
Either work in somebodies business to get the experience - or learn on your own dime -- and accept the consequences for your mistakes
If your "brilliant" you can fly by the seat of your pants to close and complete (closing to me is when the $ gets in your bank - not when they say yes or sign)
That's not coming through for me here im afraid. Dont worry - very few people are and im not either.
Take this as constructive criticism - as I dont know you from Adam. I'd suggest you look for someone in your area to mentor you a bit on sales/project such as an owner of a "small business" if you want to make a success of a local business like this. Your reputation is all in this case. Try a young Rotary or business group as your obviously not a Freemason
