You probably double-clicked an event edge or pressed 5 on the numeric keyboard. Read here how to get back https://www.vegascreativesoftware.info/us/forum/vegas-pro-faqs-and-troubleshooting-guides–104787/ point 28.
If you just want to use A and B tracks, right-click the track header and choose Expand Track Layers to expand a video track to reveal three subtracks within the main track: the A roll, B roll, and transition roll.
Magix Vegas Pro 14 and 15 licenses are similar. Pls read the points 9, 10, and 11 in the link Mike K mentioned in his post in the other thread. I (and many others) have VPro 14 and 15 installed on 2 devices and can use them simultaneously.
You should get some ideas from this thread https://forums.creativecow.net/thread/24/1021405
Note that the thread title could as well be “Is there a limit on the number of machines that [Magix] Vegas Pro [14 and] 15 can be operational on?”
“Simultaneously” is actually the keyword here as Magix is different from Sony/SCS.
A Magix rep on the Magix Vegas forum 9/14/2016: The current Sony EULA stipulates the license is for one user, it can be installed on 2 PCs for the same user, and cannot be used used on 2 or more PCs at a time. https://www.sonycreativesoftware.com/corporate/eula
“Sony grants you a limited license to use the Software on two (2) computers or mobile devices, as applicable; provided that the Software may not be used on two (2) or more devices simultaneously”.