Three weeks from Marathon weekend, make sure you've embraced a major ingredient for raceway success: POSITIVE ATTITUDE. It's truly the most overlooked "intangible" you'll bring to the race April 29th.
You've been diligent with your training, experiencing a few 10-milers if pursuing the half, and 18-20 mile effort or two for the full Marathon. Now, how about adding a middle to longer effort of 'pacing' to this, or next week's training. Doesn't have to be your longest run; maybe an 8-miler at race-goal-pace (sometimes called MGP for Marathon goal pace; HMGP for half.) If you desire a 5 hour marathon, and you feel intact and ready, aim for a 16-18 miler at 11:30 pace. For a 2-hour half (9:10 or so pace) do an 8-10 miler at this pace. This will heighten your confidence, shake any lethargy from the legs if training has been much the same for awhile, and freshen your outlook. An 'altered' effort always does that. If speed is not an issue, do shorter 'pick-ups', which raise your fitness, and also lend to the same self-empowerment.
Remember not to be too ambitious; set yourself up for SUCCESS! No need to perform the whole distance you're be aiming for April 29th. You'll be ready to answer the bell raceway due to many intangibles: least of which is gratitude for simply being a part of such a memorable day in Oklahoma City! The Memorial Marathon is unlike any other race on earth! Take it all in; you'll have it forever!