Feature Slider Size of Images too small

although my photos are bigger than the minimum size required to use as a featured image (1920 by 550). They still do not appear as though they are on my blog http://rachelinwanderland.com/
Some of the features images are perfect and fill up the width of the page, but others are small and in the middle, how do I change this? and in other situations, even if the photo is too small is there a way to stretch them?

I have tried reading other posts on this forum regarding this topic but unfortunately I am a novice in html-ing and tech-lingo.

The attached photo is what the problem is

Hi @rachelinwanderland,

I hope you are well today and thank you for your question.

It seems this is happening because of the Jetpack plugin Photon module that you are using on your site so could you please try temporary deactivating it or its Photon module on your site?

This jetpack photon module is not updating the images stored on wp.com so to resolve the issue either disable this module or update the images on wp.com by contacting jetpack support team.

Best Regards,
Movin