Event/Part correction to fit bar, Cubase 4 LE

I have had Cubase 4 LE for several years without really using it, except for making simple jam tracks when practicing lead guitar and impro. Recently, I have started discovering how great and potent the program is and have begun creating more advanced stuff and whole songs - but now a problem has arisen:

When I play my guitar and generate a track, my tempo and precision will fluctuate slightly and of course not be as exact as Cubase’s 100% accurate timing (although I am an experienced guitarist :wink: ). I might start somewhat early on a bar and end slightly after the bar. When I then select said part or event for copy/paste, a minute portion in the beginning or at the end (ot both) will be cut. How do I solve this?

Any help is much appreciated.