You will be fine; at the count your vote will probably be looked at by the counter who if they think it is not valid will pass it on to be considered by a more senior officer. If your intention is clear then it counts. I think a tick is fairly clear!
It won’t matter earnshaw your vote will be counted.
Not sure mine will count for my mayoral vote as I marked my second choice in the first box instead of the second box then crossed it out and did it correctly but I have a feeling the paper will be discounted.