Any reputable shop will guarantee paint match. If it does not match, the shop takes care of it not insurance. As long as the shop agrees to match paint and do an excellent repair, the shop will take care of it. The thing is, insurance gives you a check and they probably recommended you to one of their preferred shops. Those preferred shops will accept what ins gave you. In most States, you can take your car to any shop you want to. If the shop you choose wants more money, than ins "may" pay that shop's higher estimate. I have never used a shop ins recommended. There is only one shop that I like and I know it will be more money than what ins paid me. In my past experiences, ins paid the claim in full less my deductible.
Also, I would not hold a check for that long. Usually the check is good for a certain period.