It is more likely you are watering and/or mowing incorrectly. Then you might not be fertilizing right and that would be the trifecta. There is no way to match a seeded variety with any of the sodded varieties of bermuda. Once they grow together or you get some seeded (common) bermuda in the TIF, then you have a permanent weedy look.

You should be watering deeply and infrequently. You are probably watering lightly and every day or two. Improper watering is the fastest way to get weeds. Deeply means a full inch, as measured by some empty tuna or cat food cans in the yard. Time how long it takes your sprinkler(s) to fill the cans and use that time. Infrequently means no more than once every week or two this time of year. When the temps get into the 90s, then go to once per week.

You might be mowing too high. Bermuda should be mowed at the lowest or second lowest notch on a rotary mower. If you are fertilizing right, you might need to mow 2x per week. Mowing low will cause the bermuda to grow more horizontally than vertically. This is what causes bermuda to become dense.

If you want good color and good density (to help keep weeds out), you should fertilize every month of the growing season with a high nitrogen fertilizer.