Output text between two patterns on the same line using sed command

I tried this command and only works to certain extend

input file content

this is begin not sure what is wrong end and why not

Command

cat file | sed 's/.*begin \(.*\)end/\1/'

output

not sure what is wrong and why not

desired output ( please see notes below)

not sure what is wrong 

1 - my sed command searches for the first pattern and second pattern , but omits the second pattern and prints the text. However, it also prints the rest of the line "why not". I do not want to print what comes after the second pattern only what is between the two patterns. I am not sure how to do this 2 - what id there are two "end" in the same line?

Can someone help please and provide and explain the command?

Regards