I don’t have gimp, posting a picture of the dialog box showing the options you are using may help, but it should have a scale value option somewhere. Increase that value (default is probably 1 so use maybe a 6 see how that works. Also if there is a filter selection option, try changing that value. Default is probably a 4, with 3x3, 5x5, 7x7, and 9x9 as other selections. These effects how sharp it appears, 3x3 will make it crisp, 9x9 smooth or blurry.
Good Luck
ez