Sorry about your very first road bike ride!

Can't give you any suggestions about DVDs, but I would say it sounds like you need to get fitted. Hopefully the shop where you purchased this bike can do this for you. Yes, it sounds like you need to switch out your stem, etc.

Just so you know.... the reason the handlebars on the road bikes are designed this way is because you are more aerodynamic which is important on longer rides. Another is that when you have the choice of riding in the "drops" as they are called, you are able to stretch out your lower back which is very important in long distance cycling. I've ridden many a century and a few double metrics and can say that having that option available to me has been a life saver in many cases.

Another factor to consider is what kind of pedals you are using on the new bike. Clipless pedals are designed for you to get maximum power from your pedal stroke both going up and down hills. It takes awhile to get used to them, but in the end they are worth the effort!

How much does your bike weigh? This is also a factor going up hills.

Just my 2 cents worth. I just hope you made the right decision when you decided to go with the other handlebars. I wouldn't recommend them for century rides. Hopefully someone here on the Forum can give you input on that kind of riding.