If you go up several needle sizes and just use fewer stitches, even if you get the same size blanket, I’m concerned that the end result may not be what you’re looking for. If you use needles that are much larger than suggested for the yarn weight (worsted, bulky, etc.) the resulting fabric would be very loose and drapey. So if you used size 10 needles on a dk or sport weight yarn, I think the stitches would be very large, and might not end up making a very warm blanket.
For quick knit blankets that you can do on large size needles, bulky yarns would probably work the best. But for something that’s supposed to have size 5 needles, I’m not sure if there’s much you can do. If you were willing to start over, you could probably double your yarn and go up in needle sizes, but I don’t think there’s anything that can help with the progress you’ve already made.
Don’t give up, knitting is totally worth it. And please don’t forget to enjoy the process!!! Good luck