Opened file and lines have extended,

I opened my file and all my lines that I have drawn have somehow extended and the I cannot change them. I have lost work and it has all been changed.

HELP!! Uni assignment due Wednesday and have lost all this work

That looks like a display problem.
Are you running an old Mac with an Nvidia display card?
Maybe an older Intel 6000 or 6100?
We are seeing problems with these older cards. It seems Apple is dropping the ball for support on them.

If this is Rhino V6, please run the SystemInfo command and return the results. Hopefully something obvious pops out.