Did you really trimmed it (set start and end and press DOIT)? If so then welcome onboard

Its a bug that sometimes happen. there are two methods to get rid of the waste on the sample.
You can either use a.) delete zone or b.) copy zone
a.) in trim mode press F3 (znEDIT). Now set start and end so that you mark the part you want to GET RID OF. BTW you can't use the pads here to listen to the sound, you need to press F6 (PLAY X). Now hit F5, choose delete zone and DOIT
b.) same as a but now you choose the part you want TO KEEP. Hit F5, choose ZONE->NEW SAMPLE, give it a new name (don't forget to hit enter after naming

and DOIT. Then delete the whole sample and use the copy instead.
peace