Please do not post serial numbers, order numbers, email address, phone numbers or other confidential information. This is a public forum and you are likely to lose control of your product or be spammed.
Did you try copy and pasting the entire number serial number into the activation dialog?
Welcome to the Magix user to user forums, not a contact for Magix Support.
First, you will see I have removed the confidential serial key from your post. This is a public forum so confidential data like serial/activation keys and email addresses should never be posted here. Doing so risks your account and software being hijacked and your email Inbox being spammed!
When you first opened the app you should have seen a screen which asked you to enter your serial number or continue with the trial ( can't remember the exact wording, sorry). I'm guessing you selected the enter your serial number/register alternative, where the number you have,, beginning TRIALC would have been rejected. (That screen would have automatically had a number beginning P3 - .)
You need to continue the trail which will open a screen where you enter the number you have. The TRIALC will already be showing, you simply need to carefully enter the actual numbers.