How to extend range of clips in timeline created by i/o points FCPX

I went through my clips and made rough selections using in and out points (i & o) and then inserting the selections into my timeline (e & w). I can shorten them in my timeline, but can't extend them. It seems like when I put in and out points, it makes a distinct clip that isn't linked the rest of the clip? Is there an easy fix, or do I need to make longer clips? Thank you!