borrowed a copy and impressed but the objected i printer sthe solid straight line at the back has a empty line in the middle which makes it a little weak the infill does not seem to fill this bit if fills the sides ok

this line would be on my x axis when printing on prusa i3 any ideas

Don't really see it on that photo, it's kind of blurry.

Anyway, if it's not a printer-error you can activate "Allow gap fill when necessary" under the "advanced" tab.

That is a setting that fills small gaps on thin walls if the perimeters are not wide enough to fill all.

If it's something like this where you have a gap in a thin part, I always lower the perimeter numbers and thus it will infill it when I set infill to solid.

Then you will see something like the second photo. I was unaware of the gap filling that the other user mentioned, I will have to try that one myself