JCT Minor Works - Queries

So the contract is for 100k, and the client has issued the contract award for 100k. Note the official contract needs to be finalised. The client provided a pricing document with quantities, and we filled in the costs totalling the 100k price.

The client noted 5k as a Provisional sum (PS) for an item. (Fine)

The client states the 10k contingency sum is only useable if instructed by the Contract Administrator. Is this enforceable as we were under the impression as Minor Works is a lump sum contract, the Contingency risk is owned by the contractor?

There is also an error in the tender document client asked for a credit amount due to scrap materials. This credit amount has been inputted as a double negative, which added 10k to the contract sum instead of reducing it. As the contract award has been issued at 100k, and the error has only just been identified, what is the most likely course of action? Initial thoughts are, as it’s a lump sum price contract, and the mistake was not identified until the contract award the final agreed lump sum amount takes priority over the price breakdown.

Note since we quoted, the site has become overgrown, particularly from a bush; removal of the bush was not part of the original scope, and we are not able to continue the works unless the bush is removed. Is this an entitlement to variation as it would essentially be an amendment to employer requirements?

Curious to thoughts on the above issues?