I have been playing 3yrs now, and can only throw 300ft, so I can relate to where you are with your distance. I'm not a great putter either, but have made some big strides with that this year. The main difference with me is that I am a dominant backhand thrower. I only throw forehand if there is no alternative.
Although I don't throw that far, I've been able to lower my scores by focusing on a few key points, hopefully this will be of some help to you, too.
1) Putting is a major key to lowering your scores, spend time practicing putts. I have found
PerfectPutt 360 to be the most effective method for helping me with putting. You can play a full game in 20 minutes or so, and you end up throwing 100 putts. Do this a couple times a week, and you will see improvement. Maybe it doesn't work for everyone, but it really helped me a lot.
2) Better putting isn't going to come quickly or easily, it comes from a lot of practice. So in the meantime (while you're working on the putting), focus on your approach shots. If you're only throwing 300ft, then you are a lot like me in the since that you are throwing a drive, an approach, and putting for par (depending on the length/layout of the courses you're playing). If you want to score better, you have to put your approach shot within a range where you can make your par.
Instead of thinking "birdie" from 50-100ft, think par. Don't try to make the shot, try to putt the disc under the basket and leave yourself and easy putt for par. As your putting improves, you'll be able to be more aggressive on your approach.
These are the big things that have helped lower my scores. I am probably throwing 30ft farther on average this year, but contribute my improvement much more to better putting and a strong approach than the added distance.