Answer: Since the damage sounds fairly minor, I would expect the plants to recover assuming they were healthy otherwise. The symptoms you describe could be the result of a number of things. It could be "fertilizer burn" although that dilution was fairly mild. It could also be sunscald if it was applied on a sunny day when temperatures were high. Finally, it is always a good idea to test any new product or concoction on a few leaves and wait a few days to see if there are any negative effects. Then, if it seems okay, treat the whole plant.
However, it could also simply be drought stress. You might want to make sure that your plants are receiving ample water during the heat of the summer. Roses need, as a rule of thumb, an inch or two a week and Japanese maples also appreciate an evenly moist and cool yet well drained soil. Both types of plants do well with several inches of organic mulch and deep watering rather than frequent light sprinklings.
With regard to the bloom size, it is true that roses produce the largest showiest blooms when they are in the peak of health, so it is possible your roses have not established as well as they might have. (It is also possible that tags were switched at the nursery, that is something you would need to discuss with them if the size is truly unusually small.)
Again, water plays a very large role in successful planting, as do soil preparation and ongoing care. Roses do best in a rich, evenly moist yet well drained soil well amended with organic matter such as compost, rotted leaves, or aged stable manure and bedding. Additional amendments such as a balanced fertilizer would be added according to the results of soil tests. Your County Extension should be able to assist you with soil testing and interpreting the results, as might the nursery where you purchased the plants. Ongoing care would include removing spent flowers and monitoring for pests and diseases.... and possibly fertilizing as indicated by the soil tests.
Good luck with your plants!
Q&A Library Searching Tips