I have just setup an Azure cloud trial account for my application that solves complex problem.
Solution is working but too slow.
Limit is 20 instances - why? how to make more?
also instances are "small", how can I make "big"
If Azure not scalable, what cloud is?
During "Free" trial period, you get limited resources so that you can evaluate whether Azure is right for your business needs. Also the limit of 20 instances is by default so that you don't accidently overrun the cost (there are a lot of users including myself who have been affected by this where we ran the stuff without fully understanding the cost implications).
You could contact support to get the limit increased but I doubt that they will do it for a trial account. My guess is that you would need to purchase a subscription first to get the quota increased.