Gaps are DT growing pains. My suggestion is before spoiling a lot of good wood, to get some el cheapo used wood, pine, or whatever you can get for free, or really low cost.
Once you have a cheap wood supply, spend some time doing prep work so ALL of the stock is same size, true and flat. I believe more than half the problems with joinery are people trying to join wood that doesn't want to go together.
After your prep journey is over start cutting one corner a day. I still have my very first corner as a reminder of how bad I was starting out, and I affectionately call it Punkin Teeth, cause it is one gappy SOB. Most people after a week, 2 at the most are cutting pretty fair DT's and corners are starting to look decent. To do a corner I would grab 2 pieces of stock at least 3" wide, and only about 5 or 6" long. Then you literally just make a corner. I'd also suggest starting with through DT's and do your 1/2 blinds later, once you had throughs down pat.
Don't be in a rush, and enjoy the journey. Return with questions as you have them, take pics as you go so you have a record to look back at. If you stick with them, they will provide a smile some time in the future.
Good lighting, and having something like a Moxon vise to hold the work really do help. Other stuff, sharp saw that you enjoy holding. A good layout gauge. and really sharp, and easily held chisels for chopping, and paring your waste.