Have you measured the dimensions of all the windows that you want to tint, especially their width?
That would let you know if the 50 x 300 cm sheet is big enough to cover all that you need but I don't think that 3 metres would be long enough if you add up all the widths of the windows, plus allowing a bit of overhang on each side to allow for full coverage of the window making it easier to cut to the exact shape.
There may be enough if only using a 10cm strip on the front windscreen but then the other windows need to be approx. <38cm in height, at least for the length of the width of the windscreen, to make the remainder of the tint i.e. length of windscreen tint minus 10cm height, which is used for the windscreen, usable for the other windows