Illustrator How I delete that ii excess from my file?

[Jesica]

Hi I am jesica,I am happy to be here.I make a design with the flare tool but I need the half in my file,the rest which excess from the file I do't need.I try to delete it with eraser and lasso tool but the result isn't the desired.
If someone knows something to suggest I ll appreciate.:idea:

 

[ibis]

make new layer
resize it and position to fit your needs
flatten the image